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 A055263 #14 Feb 19 2024 01:59:10
%S A055263 0,1,3,6,1,6,3,1,9,9,10,3,6,10,6,3,10,9,9,10,3,6,10,6,3,10,9,9,10,12,
%T A055263 6,10,6,12,10,9,9,10,12,6,10,6,12,10,9,9,10,12,6,10,6,12,10,9,9,10,12,
%U A055263 15,10,15,12,10,9,9,10,12,15,10,15,12,10,9,9,10,12,15,10,15,12,10,9,9,10
%N A055263 a(n) = Sum of digits of (n + a(n-1)).
%C A055263 If n=0 or 8 mod 9, then a(n)=0 mod 9; if n=1, 4 or 7 mod 9, then a(n)=1 mod 9; if n=2 or 6 mod 9, then a(n)=3 mod 9; if n=3 or 5 mod 9, then a(n)=6 mod 9.
%H A055263 Harvey P. Dale, <a href="/A055263/b055263.txt">Table of n, a(n) for n = 0..1000</a>
%F A055263 a(n) = A007953(A055262(n)) = A007953(n + a(n-1)).
%e A055263 a(13)=10 because a(12)=6, 13 + 6 = 19 and 1 + 9 = 10.
%t A055263 nxt[{n_,a_}]:={n+1,Total[IntegerDigits[n+a+1]]}; Transpose[NestList[nxt,{0,0},90]][[2]] (* _Harvey P. Dale_, Aug 11 2016 *)
%Y A055263 Cf. A055262, A055264.
%K A055263 base,easy,nonn
%O A055263 0,3
%A A055263 _Henry Bottomley_, May 08 2000
%E A055263 More terms from _Paolo P. Lava_, Jul 31 2007