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 A048643 #8 Oct 02 2015 10:12:02 %S A048643 0,0,1,0,12,132,540,0,20160,423360,8164800,125193600,1172102400, %T A048643 11935123200,76281004800,0,10461394944000,428917192704000, %U A048643 14781951055872000,429147343392768000,14090871305871360000,461146030563778560000,13730871481551544320000,390084405122331279360000 %N A048643 Differences between partial products of Gray code (A048642) and factorials (A000142). %C A048643 a((2^n)-1) = 0 for all n. %F A048643 a(0) = 0, a(n) = product(XORnos(j, floor(j/2)), j=1..n) - n!. %F A048643 a(n) = A048642(n) - A000142(n). %o A048643 (PARI) a(n) = prod(i=1, n, bitxor(i, i>>1)) - n!; \\ _Michel Marcus_, Oct 02 2015 %Y A048643 Cf. A000142, A048642, A048644. %K A048643 easy,nonn %O A048643 0,5 %A A048643 _Antti Karttunen_, Jul 14 1999 %E A048643 More terms from _Michel Marcus_, Oct 02 2015