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 A256277 #24 Sep 08 2022 08:46:11
%S A256277 2,1,6,7,10,1,12,1,18,19,22,6,11,1,30,9,15,1,15,1,42,15,46,29,36,1,27,
%T A256277 55,58,1,14,19,66,21,70,1,32,35,78,43,82,40,60,1,7,60,70,1,18,1,102,
%U A256277 96,106,1,39,1,17,96,3,111,84,31,126,84,130,37,30,1
%N A256277 C(2*n,n) mod 2*n+1.
%C A256277 a(n) == (-1)^n (mod 2*n+1) if 2*n+1 is prime or is in A163209.
%C A256277 a(n) = 0 for n in A073076.
%H A256277 Robert Israel, <a href="/A256277/b256277.txt">Table of n, a(n) for n = 1..10000</a>
%p A256277 seq(binomial(2*n,n) mod (2*n+1), n=1..100); # _Robert Israel_, Jun 12 2015
%t A256277 Table[Mod[Binomial[2 n, n], 2 n + 1], {n, 200}] (* _Vincenzo Librandi_, May 03 2016 *)
%o A256277 (Magma) [Binomial(2*n, n) mod (2*n+1): n in [1..70]]; // _Vincenzo Librandi_, May 03 2016
%Y A256277 Cf. A000984, A001405, A059288, A053214, A073076, A163209.
%K A256277 nonn
%O A256277 1,1
%A A256277 _Robert Israel_, Jun 12 2015