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 A072118 #13 May 01 2025 08:24:53 %S A072118 1,2,5,224,672,2737152,8895744,474439680,130660687872, %T A072118 4513732853760000,15798064988160000,894413525483520000, %U A072118 3194334019584000000,27610545531676262400000,8107146431738442547200000,7569213421444268241715200000,27753782545295650219622400000 %N A072118 a(n) = (2*n)!/core(n!)^2/(n+1) where core(x) is the squarefree part of x. %H A072118 Amiram Eldar, <a href="/A072118/b072118.txt">Table of n, a(n) for n = 1..251</a> %t A072118 f[p_, e_] := p^Mod[e, 2]; a[1] = 1; a[n_] := (2*n)! / ((Times @@ f @@@ FactorInteger[n!])^2 * (n+1)); Array[a, 17] (* _Amiram Eldar_, May 01 2025 *) %o A072118 (PARI) a(n) = (2*n)!/core(n!)^2/(n+1); %Y A072118 Cf. A007913, A055204. %K A072118 easy,nonn %O A072118 1,2 %A A072118 _Benoit Cloitre_, Jun 19 2002