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Functional Equation!
EthanWYX2009   5
N a few seconds ago by Miquel-point
Source: 2025 TST 24
Find all functions $f:\mathbb Z\to\mathbb Z$ such that $f$ is unbounded and
\[2f(m)f(n)-f(n-m)-1\]is a perfect square for all integer $m,n.$
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EthanWYX2009
Mar 29, 2025
Miquel-point
a few seconds ago
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Sum of max of some sequences is sum of powers
Miquel-point   0
Apr 6, 2025
Source: Romanian IMO TST 1981, Day 3 P1
Consider the set $M$ of all sequences of integers $s=(s_1,\ldots,s_k)$ such that $0\leqslant s_i\leqslant n,\; i=1,2,\ldots,k$ and let $M(s)=\max\{s_1,\ldots,s_k\}$. Show that
\[\sum_{s\in A} M(s)=(n+1)^{k+1}-(1^k+2^k+\ldots +(n+1)^k).\]
Ioan Tomescu
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Miquel-point
Apr 6, 2025
0 replies
Sum of max of some sequences is sum of powers
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Source: Romanian IMO TST 1981, Day 3 P1
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Miquel-point
492 posts
#1 • 1 Y
Y by PikaPika999
Consider the set $M$ of all sequences of integers $s=(s_1,\ldots,s_k)$ such that $0\leqslant s_i\leqslant n,\; i=1,2,\ldots,k$ and let $M(s)=\max\{s_1,\ldots,s_k\}$. Show that
\[\sum_{s\in A} M(s)=(n+1)^{k+1}-(1^k+2^k+\ldots +(n+1)^k).\]
Ioan Tomescu
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