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 A068878 #19 May 05 2025 05:20:57
%S A068878 2,24,60,720,40320,181440,3628800,479001600,3113510400,87178291200,
%T A068878 20922789888000,177843714048000,6402373705728000,2432902008176640000,
%U A068878 25545471085854720000,1124000727777607680000,620448401733239439360000,7755605021665492992000000,403291461126605635584000000
%N A068878 Denominators of nonzero terms in the expansion of sin(x)+exp(x)-1-2*x.
%F A068878 a(3k+1)=(4k+2)!, a(3k+2)=(4k+4)!, a(3k+3)=(4k+5)!/2.
%F A068878 Sum_{n>=1} 1/a(n) = e + sin(1) - 3 = A001113 + A049469 - 3 = A348374 - 3. - _Amiram Eldar_, May 05 2025
%t A068878 Select[CoefficientList[Series[Sin[x] + Exp[x] - 1 - 2 x, {x, 0, 25}], x], # != 0 &] // Denominator
%t A068878 (* second program: *)
%t A068878 a[n_] := Switch[Mod[n, 3], 1, ((4*n+2)/3)!, 2, ((4*n+4)/3)!, 0, ((4*n+3)/3)!/2]; Array[a, 17] (* _Amiram Eldar_, May 05 2025 *)
%Y A068878 Cf. A001113, A049469, A348374.
%K A068878 easy,nonn
%O A068878 1,1
%A A068878 _Benoit Cloitre_, Mar 29 2002
%E A068878 Name clarified by _Sean A. Irvine_, Mar 19 2024
%E A068878 More terms from _Amiram Eldar_, May 05 2025