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 A028576 #11 Oct 30 2018 03:34:57
%S A028576 1,4,33,304,3175,35556,420665,5176000,65664000,853367900,11309870605,
%T A028576 152342891952,2080240006923,28738242567524,401024083514775,
%U A028576 5645275548076800,80084088088568947,1143862232096407392,16437995698573558421,237520818846111947600
%N A028576 a(n) = (1/(4*n)) * Sum_{d|n} mu(n/d) * binomial(2*d, d)^2.
%o A028576 (PARI) a(n) = sumdiv(n, d, moebius(n/d)*binomial(2*d, d)^2)/(4*n) \\ _Michel Marcus_, Jun 15 2013
%K A028576 nonn
%O A028576 1,2
%A A028576 Lionel Levine (levine(AT)ultranet.com)