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 A343156 #32 Dec 31 2023 12:35:25 %S A343156 0,0,1,0,1,0,1,1,2,0,1,0,2,4,1,0,1,0,2,1,1,0,1,1,4,1,2,0,2,0,1,1,5,3, %T A343156 1,0,2,1,2,0,2,0,1,4,1,0,1,1,2,1,4,0,1,2,2,2,1,0,2,0,3,1,1,3,1,0,5,3, %U A343156 1,0,1,0,2,4,2,2,2,0,2,1,1,0,2,3,2,3,1,0,2,64,1,1,2,4,1,0,2,1,2 %N A343156 Starting at n, a(n) = number of iterations of the map x -> A084317(x) (concatenate distinct prime factors of x) required to reach a prime, or -1 if no prime is ever reached. %C A343156 Judging by the behavior of similar sequences, it is likely that almost all values of a(n) are -1. n = 407 (see A343157) seems to be the first open case. %D A343156 Eric Angelini, W. Edwin Clark, Hans Havermann, Frank Stevenson, Allan C. Wechsler, and others, Postings to Math Fun mailing list, April 2021. %H A343156 Hans Havermann, <a href="/A343156/b343156.txt">Table of n, a(n) for n = 2..406</a> %e A343156 10 = 2*5 -> 25 = 5^2 -> 5, prime, taking two steps, so a(10)=2. %e A343156 a(91) = 64: see A084319. %Y A343156 Cf. A084317, A037274, A037276, A084319, A195264, A343157. %Y A343156 See A343158 for when k first appears. %K A343156 nonn,base %O A343156 2,9 %A A343156 _N. J. A. Sloane_, Apr 07 2021