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 A378069 #3 Dec 14 2024 18:18:40
%S A378069 0,1,3,13,45,181,658,2605,9705,38251,144606,569317,2173262,8556822,
%T A378069 32890068,129565485,500583105,1973295775,7654363750,30194784763,
%U A378069 117497078842,463820452602,1809540528588,7147843461733,27946421773270,110458073192026,432648616232028
%N A378069 a(n) = Sum_{k=0..n} binomial(n, floor(k/2 - 1/2)) * binomial(n, ceiling(k/2 - 1/2)).
%p A378069 a := n -> add(binomial(n, floor(k/2 - 1/2))*binomial(n, ceil(k/2 - 1/2)), k=0..n):
%p A378069 seq(a(n), n = 0..26);
%Y A378069 Cf. A007318, A005566, A378070.
%K A378069 nonn,easy
%O A378069 0,3
%A A378069 _Peter Luschny_, Dec 14 2024