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 A012007 #24 May 22 2017 13:01:56
%S A012007 1,0,3,30,693,25260,1351383,99680490,9695756073,1202439837720,
%T A012007 185185594118763,34674437196568950,7757267081778543453,
%U A012007 2043536254646561946180,626129820701814932734143,220771946624511552276841410,88759695789769644718332394833
%N A012007 cosh(log(cos(x))) = 1+3/4!*x^4+30/6!*x^6+693/8!*x^8+25260/10!*x^10...
%F A012007 a(n) = (1/2)*((-1)^n+A000364(n)). Also cosh(log(cos(x))) = 1/2*(cos(x)+1/cos(x)) is the reciprocal of the e.g.f. of A012009. - _Peter Bala_, Dec 02 2011
%t A012007 terms = 15; s = Cosh[Log[Cos[x]]] + O[x]^(2*terms); CoefficientList[s, x^2] * Table[(2n)!, {n, 0, terms-1}] (* _Jean-François Alcover_, May 22 2017 *)
%Y A012007 Cf. A012003, A012008, A012009.
%K A012007 nonn
%O A012007 0,3
%A A012007 Patrick Demichel (patrick.demichel(AT)hp.com)
%E A012007 Confirmed by _N. J. A. Sloane_, Dec 17 2011