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 A100676 #17 Oct 26 2019 16:30:24
%S A100676 1,1,2,3,4,5,7,13,10,10,31,11,15,27,20,48,67,17,33,19,66,33,144,23,81,
%T A100676 40,40,120,48,29,146,176,260,878,100,71,176,37,70,78,420,41,144,43,
%U A100676 274,172,189,47,407,73,209,132,266,53,235,364,478,169,105,59,411,61,207,479
%N A100676 a(1) = 1; a(n+1) = Sum_{k=1..n} a(gcd(a(k),n)).
%H A100676 Ivan Neretin, <a href="/A100676/b100676.txt">Table of n, a(n) for n = 1..10000</a>
%p A100676 a[1]:=1: for n from 2 to 75 do b[n]:=[seq(a[gcd(a[k],n-1)],k=1..n-1)]: a[n]:=sum(b[n][j],j=1..nops(b[n])) od: seq(a[n],n=1..75);
%t A100676 a[1] = 1; a[n_] := a[n] = Plus @@ a /@ GCD[Table[a[i], {i, n - 1}], n - 1]; Table[ a[n], {n, 64}] (* _Robert G. Wilson v_, Dec 09 2004 *)
%o A100676 (PARI) first(n)=my(v=vector(n)); v[1]=1; for(i=1,n-1,v[i+1]=sum(k=1,i,v[gcd(v[k],i)])); v \\ _Charles R Greathouse IV_, Apr 05 2016
%Y A100676 Cf. A056144.
%K A100676 nonn
%O A100676 1,3
%A A100676 _Leroy Quet_, Dec 06 2004
%E A100676 More terms from _Emeric Deutsch_ and _Robert G. Wilson v_, Dec 09 2004