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 A232701 #17 Mar 08 2025 18:20:47 %S A232701 0,1,3,9,105,315,4095,11025,348705,1545075,17931375,93087225, %T A232701 3764185425,45589819275,1060569885375,15877899662625,900941666625, %U A232701 5722531807867875,90088576482279375,1688777976676415625,18148954872023600625,320586579951629866875,11054393914490520969375 %N A232701 a(n) = (2*n-1)!! mod n!, where double factorial is A006882. %C A232701 (2n-1)!! is the product of first n odd numbers. %e A232701 a(4) = 1*3*5*7 mod (1*2*3*4) = 105 mod 24 = 9. %t A232701 o = 1; Reap[For[n = 1, n <= 99, n += 2, o *= n; m = Mod[o, (Quotient[n, 2] + 1)!]; Sow[m]]][[2, 1]] (* _Jean-François Alcover_, Oct 05 2017, translated from _Alex Ratushnyak_'s Python code *) %o A232701 (Python) %o A232701 import math %o A232701 o=1 %o A232701 for n in range(1,99,2): %o A232701 o*=n %o A232701 print(o % math.factorial(n//2+1), end=', ') %Y A232701 Cf. A006882, A232618, A024502 (floor((2*n-1)!! / n!)). %K A232701 nonn %O A232701 1,3 %A A232701 _Alex Ratushnyak_, Nov 28 2013