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 A384443 #12 Jun 20 2025 18:52:10
%S A384443 1,2,3,1,5,1,7,1,1,1,1,2,3,1,5,1,7,1,1,2,2,4,6,2,10,2,14,2,2,3,3,6,9,
%T A384443 3,15,3,21,3,3,1,1,2,3,1,5,1,7,1,1,5,5,10,15,5,25,5,35,5,5,1,1,2,3,1,
%U A384443 5,1,7,1,1,7,7,14,21,7,35,7,49,7,7,1,1,2,3,1
%N A384443 a(n) is the product of the prime digits of n; or 1 if n contains no prime digits.
%H A384443 Felix Huber, <a href="/A384443/b384443.txt">Table of n, a(n) for n = 1..10000</a>
%e A384443 a(2025) = 2*2*5 = 20.
%p A384443 A384443:=n->mul(select(isprime,convert(n,'base',10)));seq(A384443(n),n=1..84);
%t A384443 a[n_]:=If[ContainsAny[IntegerDigits[n],{2,3,5,7}],Times@@Select[IntegerDigits[n],PrimeQ],1];Array[a,100] (* _James C. McMahon_, Jun 20 2025 *)
%o A384443 (PARI) a(n) = vecprod(select(isprime, digits(n))); \\ _Michel Marcus_, Jun 04 2025
%Y A384443 Cf. A002110, A007947, A007954, A384444, A384445, A384505.
%K A384443 nonn,base,easy
%O A384443 1,2
%A A384443 _Felix Huber_, Jun 03 2025