A384443 a(n) is the product of the prime digits of n; or 1 if n contains no prime digits.

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, 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, 5, 1, 7, 1, 1, 7, 7, 14, 21, 7, 35, 7, 49, 7, 7, 1, 1, 2, 3, 1

Offset: 1

Author

Felix Huber, Jun 03 2025

Keywords

• nonn
• base
• easy

Examples

			a(2025) = 2*2*5 = 20.
		

Links

• Felix Huber, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A002110, A007947, A007954, A384444, A384445, A384505.

Programs

Maple

A384443:=n->mul(select(isprime,convert(n,'base',10)));seq(A384443(n),n=1..84);

Mathematica

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 *)

PARI

a(n) = vecprod(select(isprime, digits(n))); \\ Michel Marcus, Jun 04 2025