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 A227415 #24 Dec 10 2024 14:32:27 %S A227415 0,0,1,2,7,3,9,69,177,60,2715,4500,42975,104580,91665,186795,3493665, %T A227415 13497435,97345395,442245825,2601636975,13003053525,70985324025, %U A227415 64585694250,57891366225,3576632909850,9411029102475,147580842959550,476966861546175,5708173568847750 %N A227415 a(n) = (n+1)!! mod n!!. %C A227415 a(n) is divisible by A095987(n+1), and is nonzero for n > 1. - _Robert Israel_, Mar 10 2016 %H A227415 Robert Israel, <a href="/A227415/b227415.txt">Table of n, a(n) for n = 0..800</a> %F A227415 a(n) = A006882(n+1) mod A006882(n). %e A227415 a(4) = 5*3 mod 4*2 = 15 mod 8 = 7. %p A227415 seq(doublefactorial(n+1) mod doublefactorial(n), n=0..100); # _Robert Israel_, Mar 10 2016 %o A227415 (Python) %o A227415 for n in range(2, 77): %o A227415 prOdd = prEven = 1 %o A227415 for i in range(1, n, 2): prOdd *= i %o A227415 for i in range(2, n, 2): prEven *= i %o A227415 if n&1: print(prEven % prOdd, end=', ') %o A227415 else: print(prOdd % prEven, end=', ') %Y A227415 Cf. A006882, A095987. %Y A227415 Cf. A007911: (n-1)!! - (n-2)!! %Y A227415 Cf. A007912: (n-1)!! - (n-2)!! (mod n). %Y A227415 Cf. A060696: (n-1)!! + (n-2)!! except first two terms. %K A227415 nonn,easy %O A227415 0,4 %A A227415 _Alex Ratushnyak_, Jul 10 2013