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 A306184 #26 May 29 2025 13:27:40 %S A306184 1,7,9,177,2715,42975,91665,3493665,97345395,2601636975,70985324025, %T A306184 57891366225,9411029102475,476966861546175,20499289200014625, %U A306184 847876038362978625,35160445175104123875,1487419121780448231375,945654757149212735625,357657177058846280240625 %N A306184 a(n) = (2n+1)!! mod (2n)!! where k!! = A006882(k). %C A306184 a(n) is divisible by A049606(n). - _Robert Israel_, Jan 28 2019 %H A306184 Robert Israel, <a href="/A306184/b306184.txt">Table of n, a(n) for n = 1..403</a> %F A306184 a(n) = A006882(2*n+1) mod A006882(2*n). %e A306184 a(3) = A006882(7) mod A006882(6) = (7*5*3) mod (6*4*2) = 105 mod 48 = 9. %p A306184 f:= n -> doublefactorial(2*n+1) mod doublefactorial(2*n): %p A306184 map(f, [$1..40]); # _Robert Israel_, Jan 28 2019 %t A306184 Mod[#[[2]],#[[1]]]&/@Partition[Range[2,42]!!,2] (* _Harvey P. Dale_, May 29 2025 *) %o A306184 (Python) %o A306184 o=e=1 %o A306184 for n in range(2, 99, 2): %o A306184 o*=n+1 %o A306184 e*=n %o A306184 print(o%e, end=', ') %Y A306184 Cf. A006882, A049606, A122649, A129890, A232617, A232618, A306185. %K A306184 nonn %O A306184 1,2 %A A306184 _Alex Ratushnyak_, Jan 27 2019