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 A046503 #18 Feb 16 2025 08:32:39 %S A046503 47,59,79,89,97,139,149,157,179,193,197,227,229,239,263,283,293,337, %T A046503 347,353,359,367,373,383,389,419,433,443,449,463,479,487,491,499,571, %U A046503 577,593,619,643,661,673,683,691,719,733,743,751,757,797,823,829,839 %N A046503 Primes with multiplicative persistence value 3. %H A046503 Robert Israel, <a href="/A046503/b046503.txt">Table of n, a(n) for n = 1..10000</a> %H A046503 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/MultiplicativePersistence.html">Multiplicative Persistence</a> %e A046503 47 -> 4 * 7 -> [ 28 ] -> 2 * 8 -> [ 16 ] -> 1 * 6 -> [ 6 ] -> one digit in three steps. %p A046503 filter:= proc(n) local L; %p A046503 if not isprime(n) then return false fi; %p A046503 L:= convert(convert(n,base,10),`*`); if L < 10 then return false fi; %p A046503 L:= convert(convert(L,base,10),`*`); if L < 10 then return false fi; %p A046503 L:= convert(convert(L,base,10),`*`); evalb(L < 10) %p A046503 end proc: %p A046503 select(filter, [seq(i,i=11..1000,2)]); # _Robert Israel_, Jun 05 2018 %t A046503 pr3Q[n_] := Length[NestWhileList[Times @@ IntegerDigits[#] &, n, # > 9 &]] == 4; Select[Prime[Range[147]], pr3Q] (* _Jayanta Basu_, Jun 26 2013 *) %Y A046503 Cf. A046500, A046512. %K A046503 nonn,base %O A046503 1,1 %A A046503 _Patrick De Geest_, Sep 15 1998