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 A059688 #13 Apr 03 2023 10:36:09
%S A059688 5,2,5,2,5,0,0,0,5,2,0,0,3,0,5,2,2,0,0,0,0,0,3,6,0,0,0,2,0,2,0,2,0,0,
%T A059688 0,0,0,0,3,2,6,0,2,0,0,0,0,0,2,0,2,2,0,2,0,2,0,0,0,2,0,2,0,0,0,0,0,0,
%U A059688 2,0,0,6,0,0,0,2,0,0,0,0,2,0,2,0,0,2,0,0,0,0,2,2,0,2,0,2,4,0,0,0,0,0,2,0,0
%N A059688 Length of Cunningham chain containing prime(n) either as initial, internal or final term.
%C A059688 The length of a chain is measured by the total number of terms including the end points. a(n)=0 means that prime(n) is neither Sophie Germain nor a safe prime (i.e. it is in A059500).
%H A059688 C. K. Caldwell, <a href="https://t5k.org/glossary/page.php/CunninghamChain">Cunningham Chains</a>
%H A059688 W. Roonguthai, <a href="http://ksc9.th.com/warut/cunningham.html">Yves Gallot's Proth.exe and Cunningham Chains</a>
%e A059688 For all of {2,5,11,23,47}, i.e. at positions {j}={1,3,5,9,15} a(j)=5. Similarly for indices of all terms in {89,...,5759} a(i)=6. No chains are intelligible with length = 1 because the minimal chain enclose one Sophie Germain and also one safe prime. Dominant values are 0 and 2.
%Y A059688 Cf. A005384, A005385, A053176, A059452-A059456, A007700, A005602, A023272, A023302, A023330, A059500.
%K A059688 nonn
%O A059688 1,1
%A A059688 _Labos Elemer_, Feb 06 2001
%E A059688 Offset and a(5) corrected by _Sean A. Irvine_, Oct 01 2022