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 A122685 #15 Oct 21 2018 12:56:36 %S A122685 1,1,-2,6,0,120,0,5040,0,362880,0,39916800,0,6227020800,0, %T A122685 1307674368000,0,355687428096000,0,121645100408832000,0, %U A122685 51090942171709440000,0,25852016738884976640000,0,15511210043330985984000000,0,10888869450418352160768000000,0,8841761993739701954543616000000 %N A122685 a(n) = n! except that a(2) = -2 and a(2n) = 0 for n > 2. %C A122685 Same as A005212 for n > 2. - _Georg Fischer_, Oct 21 2018 %Y A122685 Cf. A005212, A009445. %K A122685 sign,easy,less %O A122685 0,3 %A A122685 _Paul Curtz_, Jul 28 2007 %E A122685 Edited by _N. J. A. Sloane_, Jul 29 2007