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 A084309 #14 May 05 2017 08:28:10
%S A084309 1,2,1,2,5,6,1,2,1,2,1,12,1,14,1,4,1,6,1,10,3,2,1,8,1,2,3,2,1,2,1,2,1,
%T A084309 2,1,6,1,2,1,4,1,6,1,4,1,2,1,6,1,2,1,2,1,2,1,2,1,2,1,20,1,2,9,2,13,2,
%U A084309 1,4,1,2,1,2,1,2,3,2,1,6,1,8,1,2,1,12,1,2,1,8,1,6,1,2,3,2,1,2,1,2,9,20,1,2
%N A084309 a(n) = gcd(prime(n)-1, n).
%H A084309 Ivan Neretin, <a href="/A084309/b084309.txt">Table of n, a(n) for n = 1..10000</a>
%p A084309 A084309:=n->gcd(ithprime(n)-1,n): seq(A084309(n), n=1..150); # _Wesley Ivan Hurt_, Feb 01 2017
%t A084309 Table[GCD[Prime[w]-1, w], {w, 128}]
%o A084309 (PARI) a(n) = gcd(prime(n)-1, n); \\ _Michel Marcus_, Feb 02 2017
%Y A084309 Cf. A084310, A084311, A084312, A084313, A084314, A084315, A084316.
%K A084309 nonn,easy
%O A084309 1,2
%A A084309 _Labos Elemer_, Jun 13 2003