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 A058005 #21 Mar 07 2025 03:00:24 %S A058005 2,2,2,2,2,12,2,2,2,4,2,4,2,4,30,2,2,12,2,20,6,4,2,12,2,4,2,56,2,4,2, %T A058005 2,6,4,14,4,2,4,2,20,2,84,2,8,90,4,2,12,2,4,6,8,2,12,2,8,6,4,2,24,2,4, %U A058005 6,2,10,132,2,4,6,20,2,36,2,4,30,8,154,12,2,20,2,4,2,56,10,4,6,88,2,20 %N A058005 a(n) = gcd(2*n, binomial(2*n, n)). %C A058005 a(n) = 2 for values like 1,2,3,4,5,7, ...; a(n) = 2n for values like 6,15,...,190. %H A058005 Amiram Eldar, <a href="/A058005/b058005.txt">Table of n, a(n) for n = 1..10000</a> %t A058005 a[n_] := GCD[2*n, Binomial[2*n, n]]; Array[a, 100] (* _Amiram Eldar_, Mar 07 2025 *) %o A058005 (PARI) a(n) = gcd(2*n, binomial(2*n, n)); \\ _Amiram Eldar_, Mar 07 2025 %Y A058005 Cf. A001405, A071416. %K A058005 nonn %O A058005 1,1 %A A058005 _Labos Elemer_, Nov 13 2000 %E A058005 Name corrected by _Hugo Pfoertner_, Mar 22 2020