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 A135207 #9 Nov 03 2024 18:09:57
%S A135207 1,1,2,9,19,40,18,28,37,45,1,2,9,46,67,81,64,55,54,73,7,36,55,49,99,
%T A135207 109,64,63,64,34,18,55,76,81,73,73,72,82,79,90,19,49,99,136,82,63,64,
%U A135207 70,54,73,40,27,82,82,72,82,70,72,91,49,36,64,91,99,145,79,126,82,58,126,28
%N A135207 a(n)=Sum_digits{n^Sum_digits[a(n-1)]}, with a(0)=1.
%H A135207 Harvey P. Dale, <a href="/A135207/b135207.txt">Table of n, a(n) for n = 0..1000</a>
%p A135207 P:=proc(n) local a,i,k,w; a:=1; print(a); for i from 1 by 1 to n do w:=0; k:=a; while k>0 do w:=w+k-(trunc(k/10)*10); k:=trunc(k/10); od; k:=i^w; w:=0; while k>0 do w:=w+k-(trunc(k/10)*10); k:=trunc(k/10); od; a:=w; print(w); od; end: P(100);
%t A135207 nxt[{n_,a_}]:={n+1,Total[IntegerDigits[(n+1)^Total[IntegerDigits[a]]]]}; NestList[nxt,{0,1},70][[;;,2]] (* _Harvey P. Dale_, Nov 03 2024 *)
%Y A135207 Cf. A047912, A066588, A108827.
%K A135207 easy,nonn
%O A135207 0,3
%A A135207 _Paolo P. Lava_ and _Giorgio Balzarotti_, Dec 03 2007