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 A057815 #16 Mar 22 2020 09:57:51 %S A057815 1,2,3,2,5,2,7,2,9,2,11,12,13,2,15,2,17,2,19,4,21,2,23,4,25,2,27,4,29, %T A057815 30,31,2,33,2,35,12,37,2,39,20,41,6,43,4,45,2,47,12,49,2,51,4,53,2,55, %U A057815 56,57,2,59,4,61,2,63,2,65,6,67,4,69,14,71,4,73,2,75,4,77,2,79,20,81,2 %N A057815 a(n) = gcd(n,binomial(n,floor(n/2))). %C A057815 For even n, a(n) is an even divisor of n. %H A057815 Hugo Pfoertner, <a href="/A057815/b057815.txt">Table of n, a(n) for n = 1..10000</a> %F A057815 a(2k+1) = 2k+1. a(2k) = A058005(k). %p A057815 swing := n -> n!/iquo(n,2)!^2: seq(igcd(n,swing(n)), n=1..82); # _Peter Luschny_, May 17 2013 %t A057815 a[n_] := GCD[n, Binomial[n, Floor[n/2]]]; Array[a, 100] (* _Jean-François Alcover_, Jun 03 2019 *) %o A057815 (PARI) a(n) = gcd(n,binomial(n, n\2)); \\ _Michel Marcus_, Mar 22 2020 %Y A057815 Cf. A001405, A049077. %K A057815 nonn %O A057815 1,2 %A A057815 _Labos Elemer_, Nov 13 2000 %E A057815 Offset changed to 1 by _Peter Luschny_, May 17 2013