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 A180637 #9 Feb 10 2019 01:50:34 %S A180637 0,3,3,3,9,3,3,6,3,3,9,3,9,3,3,6,3,3,6,3,9,3,9,3,6,3,3,3,9,3,6,9,3,6, %T A180637 3,9,3,3,6,9,3,3,6,3,6,3,9,3,9,3,3,6,9,3,3,3,6,9,3,6,3,6,9,3,6,3,3,9, %U A180637 3,3,6,9,3,9,3,9,3,9,3,3,6,3,3,6,9,3,9,3,6,9,3,6,3,3,9,3,6,9,3,6,3,6,3,6,9 %N A180637 Digital root of A179899. %C A180637 Every term after the first is 3, 6, or 9. %H A180637 Nathaniel Johnston, <a href="/A180637/b180637.txt">Table of n, a(n) for n = 1..10000</a> %p A180637 ithnonprime := proc(n)local k: option remember: if(n=1)then return 1: else k := procname(n-1)+1: while true do if(not isprime(k))then return k fi: k:=k+1: od: fi: end: A179899ind := proc(n) option remember: local k: if(n=1)then return 1:fi: for k from procname(n-1)+1 do if(ithnonprime(k) mod 2 <> 0)then return k: fi: od: end: A180637 := proc(n) if(n=1)then return 0:fi: return ((3*(ithnonprime(A179899ind(n))-1)/2 - 1) mod 9) + 1: end: seq(A180637(n),n=1..100); # _Nathaniel Johnston_, May 05 2011 %Y A180637 Cf. A179899. %K A180637 easy,nonn,base %O A180637 1,2 %A A180637 _Odimar Fabeny_, Sep 13 2010 %E A180637 Edited by _Nathaniel Johnston_, May 05 2011