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putnam_2025_a1
|
import Mathlib
set_option pp.numericTypes true
set_option pp.funBinderTypes true
set_option maxHeartbeats 0
open Classical
theorem putnam_2025_a1 (m n : β β β)
(h0 : m 0 > 0 β§ n 0 > 0 β§ m 0 β n 0)
(hm : β k : β, m (k + 1) = ((2 * m k + 1) / (2 * n k + 1) : β).num)
(hn : β k : β, n (k + 1) = ((2 * m k + 1) / (2 * n k + 1) : β).den):
{k | Β¬ (2 * m k + 1).Coprime (2 * n k + 1)}.Finite := by
sorry
|
Let $m_0$ and $n_0$ be distinct positive integers. For every positive integer $k$, define $m_k$ and $n_k$ to be the relatively prime positive integers such that $$\frac{m_k}{n_k} = \frac{2m_{k-1} + 1}{2n_{k-1} + 1}.$$ Prove that $2m_k + 1$ and $2n_k + 1$ are relatively prime for all but finitely many positive integers $k$.
|
putnam_2025_a2
|
import Mathlib
set_option pp.numericTypes true
set_option pp.funBinderTypes true
set_option maxHeartbeats 0
open Classical Set Real
theorem putnam_2025_a2 :
IsGreatest {a : β | β x β Icc 0 Ο, a * x * (Ο - x) β€ sin x} (1 / Ο) β§
IsLeast {b : β | β x β Icc 0 Ο, b * x * (Ο - x) β₯ sin x} (4 / Ο ^ 2) := by
sorry
|
Find the largest real number $a$ and the smallest real number $b$ such that $$ax(\pi - x) \le \sin x \le bx(\pi - x)$$ for all $x$ in the interval $[0, \pi]$.
|
putnam_2025_a3
|
import Mathlib
set_option pp.numericTypes true
set_option pp.funBinderTypes true
set_option maxHeartbeats 0
open Classical Finset
abbrev State (n : β) : Type := (Fin n β Fin 3) Γ Finset (Fin n β Fin 3)
abbrev State.validNext {n : β} (s : State n) : Finset (State n) :=
{s' |
s'.1 β s.2 β§
(β (i : Fin n) (Ξ΄ : ({1, -1} : Finset β€)), s'.1 i = s.1 i + Ξ΄.val β§ β j β i, s'.1 j = s.1 j) β§
s'.2 = s.2.erase s'.1}
abbrev State.init (n : β) : State n := β¨fun _ β¦ 0, Finset.univ.erase (fun _ β¦ 0)β©
abbrev Strategy (n : β) : Type := State n β State n
abbrev IsRollout {n : β} (a b : Strategy n) (s : β β State n) : Prop :=
s 0 = State.init n β§
(β i, Even i β s (i + 1) = a (s i)) β§
(β i, Odd i β s (i + 1) = b (s i))
theorem putnam_2025_a3 (n : β)
(hn : 1 β€ n):
β b : Strategy n, β a : Strategy n,
β s : β β State n, IsRollout a b s β
β k : β, Even k β§ (β i < k, s (i + 1) β (s i).validNext) β§ s (k + 1) β (s k).validNext := by
sorry
|
Alice and Bob play a game with a string of $n$ digits, each of which is restricted to be 0, 1, or 2. Initially all the digits are 0. A legal move is to add or subtract 1 from one digit to create a new string that has not appeared before. A player with no legal move loses, and the other player wins. Alice goes first, and the players alternate moves. For each $n \ge 1$, determine which player has a strategy that guarantees winning.
|
putnam_2025_a4
|
import Mathlib
set_option pp.numericTypes true
set_option pp.funBinderTypes true
set_option maxHeartbeats 0
open Classical
theorem putnam_2025_a4 :
IsLeast {k : β | k > 0 β§ β A : Fin 2025 β Matrix (Fin k) (Fin k) β, β i j, A i * A j = A j * A i β |(i : β€) - (j : β€)| β ({0, 1, 2024} : Set β€)} 3 := by
sorry
|
Find the minimal value of $k$ such that there exist $k$-by-$k$ real matrices $A_1, \ldots, A_{2025}$ with the property that $A_i A_j = A_j A_i$ if and only if $|i - j| \in \{0, 1, 2024\}$.
|
putnam_2025_b1
|
import Mathlib
set_option pp.numericTypes true
set_option pp.funBinderTypes true
set_option maxHeartbeats 0
open EuclideanGeometry Affine Simplex
theorem putnam_2025_b1 (c : EuclideanSpace β (Fin 2) β Bool)
(hc : β t : Triangle β (EuclideanSpace β (Fin 2)), c (t.points 0) = c (t.points 1) β c (t.points 0) = c (t.points 2) β
c (t.points 0) = c (circumcenter t)):
β c0 : Bool, β A, c A = c0 := by
sorry
|
Suppose that each point in the plane is colored either red or green, subject to the following condition: For every three noncollinear points $A$, $B$, $C$ of the same color, the center of the circle passing through $A$, $B$, $C$ is also this color. Prove that all points of the plane are the same color.
|
putnam_2025_a6
|
import Mathlib
set_option pp.numericTypes true
set_option pp.funBinderTypes true
set_option maxHeartbeats 0
open Classical
theorem putnam_2025_a6 (b : β β β€)
(hb0 : b 0 = 0)
(hb : β n, b (n + 1) = 2 * b n ^ 2 + b n + 1)
(k : β)
(hk : k β₯ 1):
padicValInt 2 (b (2 ^ (k + 1)) - 2 * b (2 ^ k)) = 2 * k + 2 := by
sorry
|
Let $b_0 = 0$ and, for $n \ge 0$, define $b_{n+1} = 2b_n^2 + b_n + 1$. For each $k \ge 1$, show that $b_{2^{k+1}} - 2b_{2^k}$ is divisible by $2^{2k+2}$ but not by $2^{2k+3}$.
|
putnam_2025_b2
|
import Mathlib
set_option pp.numericTypes true
set_option pp.funBinderTypes true
set_option maxHeartbeats 0
open BigOperators Real Nat Topology Rat MeasureTheory Set Real
theorem putnam_2025_b2 (f : β β β)
(hf : β x β Icc 0 1, 0 β€ f x)
(hfm : StrictMono f)
(hfc : Continuous f):
let R : Set (β Γ β) := { x | 0 β€ x.1 β§ x.1 β€ 1 β§ 0 β€ x.2 β§ x.2 β€ f x.1 }
let xβ : β := β¨ x in R, x.1
let R' : Set (β Γ β Γ β) := { x' | β x β R, β ΞΈ : β, x'.1 = x.1 β§ x'.2.1 = x.2 * cos ΞΈ β§ x'.2.2 = x.2 * sin ΞΈ }
let xβ : β := β¨ x' in R', x'.1
xβ < xβ := by
sorry
|
Let $f: [0,1] \to [0, \infty)$ be strictly increasing and continuous. Let $R$ be the region bounded by $x = 0$, $x = 1$, $y = 0$, and $y = f(x)$. Let $x_1$ be the $x$-coordinate of the centroid of $R$. Let $x_2$ be the $x$-coordinate of the centroid of the solid generated by rotating $R$ about the $x$-axis. Prove that $x_1 < x_2$.
|
putnam_2025_b3
|
import Mathlib
set_option pp.numericTypes true
set_option pp.funBinderTypes true
set_option maxHeartbeats 0
open Classical
theorem putnam_2025_b3 (S : Set β)
(hS : S.Nonempty)
(h0 : β n β S, 0 < n)
(h : β n β S, β d : β, 0 < d β d β£ 2025 ^ n - 15 ^ n β d β S)
(n : β)
(hn : 0 < n):
n β S := by sorry
|
Suppose $S$ is a nonempty set of positive integers with the property that if $n$ is in $S$, then every positive divisor of $2025^n - 15^n$ is in $S$. Must $S$ contain all positive integers?
|
putnam_2025_b4
|
import Mathlib
set_option pp.numericTypes true
set_option pp.funBinderTypes true
set_option maxHeartbeats 0
def MatrixProp (n : β) (A : β β β β β) : Prop :=
(β i j : β, 1 β€ i β i β€ n β 1 β€ j β j β€ n β i + j β€ n β A i j = 0) β§
(β i j : β, 1 β€ i β i β€ n - 1 β 1 β€ j β j β€ n β
A (i + 1) j = A i j β¨ A (i + 1) j = A i j + 1) β§
(β i j : β, 1 β€ i β i β€ n β 1 β€ j β j β€ n - 1 β
A i (j + 1) = A i j β¨ A i (j + 1) = A i j + 1)
def colSum (n : β) (A : β β β β β) (j : β) : β :=
Finset.sum (Finset.range n) (fun i => A (i + 1) j)
def colNonzeros (n : β) (A : β β β β β) (j : β) : β :=
((Finset.range n).filter (fun i => A (i + 1) j β 0)).card
def totalSum (n : β) (A : β β β β β) : β :=
Finset.sum (Finset.range n) (fun j => colSum n A (j + 1))
def nonzeroCount (n : β) (A : β β β β β) : β :=
Finset.sum (Finset.range n) (fun j => colNonzeros n A (j + 1))
theorem putnam_2025_b4 (n : β)
(hn : 2 β€ n)
(A : β β β β β)
(h : MatrixProp n A):
3 * totalSum n A β€ (n + 2) * nonzeroCount n A := by
sorry
|
For $n \geq 2$, let $A = [a_{i,j}]_{i,j=1}^n$ be an $n$-by-$n$ matrix of nonnegative integers such that: (a) $a_{i,j} = 0$ when $i + j \leq n$; (b) $a_{i+1,j} \in \{a_{i,j}, a_{i,j} + 1\}$ when $1 \leq i \leq n-1$ and $1 \leq j \leq n$; and (c) $a_{i,j+1} \in \{a_{i,j}, a_{i,j} + 1\}$ when $1 \leq i \leq n$ and $1 \leq j \leq n-1$. Let $S$ be the sum of the entries of $A$, and let $N$ be the number of nonzero entries of $A$. Prove that $S \leq \frac{(n+2)N}{3}$.
|
putnam_2025_b5
|
import Mathlib
set_option pp.numericTypes true
set_option pp.funBinderTypes true
set_option maxHeartbeats 0
open Finset ZMod Classical
theorem putnam_2025_b5 (p : β)
[hp : Fact p.Prime]
(hp3 : 3 < p):
(#{k : ZMod p | k β 0 β§ k β -1 β§ (k + 1)β»ΒΉ.val < kβ»ΒΉ.val} : β) > p / 4 - 1 := by
sorry
|
Let $p$ be a prime number greater than 3. For each $k \in \{1, \ldots, p-1\}$, let $I(k) \in \{1, 2, \ldots, p-1\}$ be such that $k \cdot I(k) \equiv 1 \pmod{p}$. Prove that the number of integers $k \in \{1, \ldots, p-2\}$ such that $I(k+1) < I(k)$ is greater than $p/4 - 1$.
|
putnam_2025_b6
|
import Mathlib
set_option pp.numericTypes true
set_option pp.funBinderTypes true
set_option maxHeartbeats 0
open BigOperators Real Nat Topology Rat
theorem putnam_2025_b6 :
IsGreatest {r : β | β g : β+ β β+, β n : β+, (g (n + 1) : β) - (g n : β) β₯ (g (g n) : β) ^ r} (1/4 : β) := by
sorry
|
Let $\mathbb{N} = \{1, 2, 3, \ldots\}$. Find the largest real constant $r$ such that there exists a function $g: \mathbb{N} \to \mathbb{N}$ such that $$g(n+1) - g(n) \geq (g(g(n)))^r$$ for all $n \in \mathbb{N}$.
|
putnam_2025_a5
|
import Mathlib
set_option pp.numericTypes true
set_option pp.funBinderTypes true
set_option maxHeartbeats 0
open Finset
def f (n : β) (s : Fin n β β€Λ£) : β :=
Finset.card {Ο : Equiv.Perm (Fin (n + 1)) |
β i : Fin n, 0 < (s i : β€) * ((Ο i.succ : β€) - (Ο i.castSucc : β€))}
theorem putnam_2025_a5
(n : β)
(hn : 1 β€ n)
(s : Fin n β β€Λ£) :
(β t : Fin n β β€Λ£, f n t β€ f n s) β
(β i : Fin n, s i = (-1) ^ (i.val + 1)) β¨ (β i : Fin n, s i = (-1) ^ i.val) := by
sorry
|
Let $b_0 = 0$ and, for $n \ge 0$, define $b_{n+1} = 2b_n^2 + b_n + 1$. For each $k \ge 1$, show that $b_{2^{k+1}} - 2b_{2^k}$ is divisible by $2^{2k+2}$ but not by $2^{2k+3}$.
|
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