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 A075423 #8 Sep 26 2015 17:24:40 %S A075423 0,1,2,1,4,5,6,1,2,9,10,5,12,13,14,1,16,5,18,9,20,21,22,5,4,25,2,13, %T A075423 28,29,30,1,32,33,34,5,36,37,38,9,40,41,42,21,14,45,46,5,6,9,50,25,52, %U A075423 5,54,13,56,57,58,29,60,61,20,1,64,65,66,33,68,69,70,5,72,73,14,37,76,77 %N A075423 rad(n) - 1, where rad(n) is the squarefree kernel of n (A007947). %C A075423 a(n) < n for all n, see A075425. %o A075423 (PARI) a(n)=factorback(factor(n)[,1])-1 \\ _Charles R Greathouse IV_, Jul 09 2013 %Y A075423 A075424(n) = a(a(n)) for n>1. %K A075423 nonn %O A075423 1,3 %A A075423 _Reinhard Zumkeller_, Sep 15 2002