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A343158 a(n) is the smallest m such that A343156(m) = n, or -1 if no such m exists.

%I A343158 #27 Jul 17 2022 02:22:38
%S A343158 2,4,10,35,15,34,190,290,303,395,130,465,553,265,195,663,218,582,481,
%T A343158 858,714,418,345,530,382,1771,1207,2098,3890,1426,2090,4834,4618,627,
%U A343158 2321,2163,326,866,3302,1298,3886,3094,1086,6130,4807,3646,5181,905,3945,5753
%N A343158 a(n) is the smallest m such that A343156(m) = n, or -1 if no such m exists.
%D A343158 Eric Angelini, W. Edwin Clark, Hans Havermann, Frank Stevenson, Allan C. Wechsler, and others, Postings to Math Fun mailing list, April 2021.
%e A343158 2 takes 0 steps to reach a prime, so a(0) = 2.
%e A343158 10 -> 25 -> 5 takes 2 steps to reach a prime (and no smaller number takes that many steps), so a(2) = 10.
%e A343158 35 -> 57 -> 319 -> 1129 takes 3 steps to reach a prime (and no smaller number takes that many steps), so a(3) = 35.
%o A343158 (PARI) is(m, n) = my(k=m); for(i=1, n, if(isprime(k), return(0), k=eval(concat(apply(t->Str(t), factor(k)[, 1]~))))); isprime(k);
%o A343158 a(n) = for(m=2, oo, if(is(m, n), return(m))); \\ _Jinyuan Wang_, Jul 16 2022
%Y A343158 Cf. A084317, A084319, A343156.
%K A343158 nonn,base
%O A343158 0,1
%A A343158 _N. J. A. Sloane_, Apr 07 2021
%E A343158 a(32)-a(42) from _Hans Havermann_, Apr 07 2021
%E A343158 a(43)-a(48) from _Hans Havermann_, Apr 08 2021
%E A343158 a(49) from _Jinyuan Wang_, Jul 16 2022