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 A217921 #7 Mar 26 2013 01:27:09 %S A217921 0,1,0,2,1,2,0,2,2,1,3,3,3,2,0,2,2,4,3,3,1,4,3,2,3,3,2,2,3,2,0,2,2,4, %T A217921 2,2,4,3,2,3,4,1,3,4,3,4,3,2,2,4,3,3,3,2,2,3,2,3,2,2,3,2,0,2,2,4,2,2, %U A217921 4,2,3,2,2,4,5,3,4,2,2,3,4,3,3,3,1,4 %N A217921 Number of steps to calculate A175872(n). %C A217921 a(A000225(n)) = 0; a(A000975(n)) = 1. %H A217921 Reinhard Zumkeller, <a href="/A217921/b217921.txt">Table of n, a(n) for n = 1..10000</a> %e A217921 n=100, 4 steps: [1,1,0,0,1,0,0]->[2,2,1,2]->[2,1,1]->[1,2]->[1,1], therefore a(100)=4, A175872(100)=2; %e A217921 n=127, no step: [1,1,1,1,1,1,1], therefore a(127)=0, A175872(127)=7; %e A217921 n=128, 2 steps: [1,0,0,0,0,0,0,0]->[1,7]->[1,1], therefore a(128)=2, A175872(128)=2; %e A217921 n=129, 2 steps: [1,0,0,0,0,0,0,1]->[1,6,1]->[1,1,1], therefore a(129)=2, A175872(129)=3; %e A217921 n=130, 4 steps: [1,0,0,0,0,0,1,0]->[1,5,1,1]->[1,1,2]->[2,1]->[1,2], therefore a(130)=4, A175872(130)=2; %e A217921 n=131, 2 steps: [1,0,0,0,0,0,1,1]->[1,5,2]->[1,1,1], therefore a(131)=2, A175872(100)=3. %o A217921 (Haskell) %o A217921 import Data.List (group, genericLength) %o A217921 a217921 n = fst $ until (all (== 1) . snd) f (0, a030308_row n) where %o A217921 f (i, xs) = (i + 1, map genericLength $ group xs) %Y A217921 Cf. A030308. %K A217921 nonn %O A217921 1,4 %A A217921 _Reinhard Zumkeller_, Mar 26 2013