This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A385554 #15 Jul 06 2025 10:06:58
%S A385554 1,10,20,20,40,200,200,200,400,400,400,400,400,400,400,400,800,800,
%T A385554 800,800,800,800,800,800,800,4000,4000,4000,4000,4000,4000,4000,8000,
%U A385554 8000,8000,8000,8000,8000,8000,8000,8000,8000,8000,8000,8000,8000,8000,8000,8000,8000,8000,8000
%N A385554 Period of {binomial(N,n) mod 10: N in Z}.
%H A385554 Jianing Song, <a href="/A385554/b385554.txt">Table of n, a(n) for n = 0..1024</a>
%F A385554 a(n) = (the smallest power of 2 > n) * (the smallest power of 5 > n) = A062383(n) * A385552(n). For the general result, see A349593.
%e A385554 For N == 0, 1, ..., 19 (mod 20), binomial(N,3) == {0, 0, 0, 1, 4, 0, 0, 5, 6, 4, 0, 5, 0, 6, 4, 5, 0, 0, 6, 9} (mod 10).
%e A385554 For N == 0, 1, ..., 39 (mod 40), binomial(N,4) == {0, 0, 0, 0, 1, 5, 5, 5, 0, 6, 0, 0, 5, 5, 1, 5, 0, 0, 0, 6, 5, 5, 5, 5, 6, 0, 0, 0, 5, 1, 5, 5, 0, 0, 6, 0, 5, 5, 5, 1} (mod 10).
%o A385554 (PARI) a(n) = if(n, (2^(logint(n,2)+1)) * (5^(logint(n,5)+1)), 1)
%Y A385554 Column 10 of A349593. A062383, A064235 (if offset 0), A385552, and A385553 are respectively columns 2, 3, 5, and 6.
%K A385554 nonn,easy
%O A385554 0,2
%A A385554 _Jianing Song_, Jul 03 2025