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 A075425 #10 Sep 26 2015 17:25:24 %S A075425 0,1,2,1,2,3,4,1,2,3,4,3,4,5,6,1,2,3,4,3,4,5,6,3,2,3,2,5,6,7,8,1,2,3, %T A075425 4,3,4,5,6,3,4,5,6,5,6,7,8,3,4,3,4,3,4,3,4,5,6,7,8,7,8,9,4,1,2,3,4,3, %U A075425 4,5,6,3,4,5,6,5,6,7,8,3,2,3,4,5,6,7,8,5,6,7,8,7,8,9,10,3,4,5,2,3,4,5,6,3 %N A075425 Number of steps to reach 1 starting with n and iterating the map n ->rad(n)-1, where rad(n) is the squarefree kernel of n (A007947). %C A075425 Sequence is defined for all n, as A075423(n) < n. %H A075425 Charles R Greathouse IV, <a href="/A075425/b075425.txt">Table of n, a(n) for n = 1..10000</a> %o A075425 (PARI) rad(n)=vecprod(factor(n)[,1]) %o A075425 a(n)=my(k);while(n>1,n=rad(n)-1;k++); k \\ _Charles R Greathouse IV_, Jul 09 2013 %o A075425 (Haskell) %o A075425 a075425 n = snd $ until ((== 1) . fst) %o A075425 (\(x, i) -> (a075423 x, i + 1)) (n, 0) %o A075425 -- _Reinhard Zumkeller_, Aug 14 2013 %K A075425 nonn %O A075425 1,3 %A A075425 _Reinhard Zumkeller_, Sep 15 2002