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 A183893 #15 Sep 08 2022 08:45:55
%S A183893 1,1,-1,-1,9,9,-73,-73,697,697,-7161,-7161,77457,77457,-868881,
%T A183893 -868881,10016241,10016241,-117935473,-117935473,1412307481,
%U A183893 1412307481,-17148100569,-17148100569,210619695913,210619695913,-2612194773481,-2612194773481,32668519882017,32668519882017,-411515480555553
%N A183893 Real part of a Gaussian integer sequence with a Gaussian integer Somos-4 Hankel transform.
%C A183893 Hankel transform of A183893(n)+I*A183894(n) is the (-4,-4) Somos-4 Gaussian integer sequence A183895(n)+I*A183896(n).
%H A183893 G. C. Greubel, <a href="/A183893/b183893.txt">Table of n, a(n) for n = 0..500</a>
%F A183893 a(n) = Re(Sum{k=0..n, C(floor((n+k)/2),k)*I^k*A000108(k)}), I=sqrt(-1).
%t A183893 Table[Re[Sum[I^k*Binomial[2*k, k]*Binomial[Floor[(n + k)/2], k]/(k + 1), {k, 0, n}]], {n, 0, 50}] (* _G. C. Greubel_, Feb 21 2018 *)
%o A183893 (PARI) for(n=0,50, print1(real(sum(k=0,n, I^k*binomial(2*k,k)* binomial( floor((n+k)/2),k)/(k+1) )), ", ")) \\ _G. C. Greubel_, Feb 21 2018
%o A183893 (Magma) [Round(Real((&+[(Sqrt(-1))^k*Binomial(2*k,k)*Binomial( Floor((n+k)/2),k)/(k+1): k in [0..n]]))): n in [0..30]]; // _G. C. Greubel_, Feb 21 2018
%K A183893 sign
%O A183893 0,5
%A A183893 _Paul Barry_, Jan 07 2011