A178327 Numbers k such that k^p+p is prime, where p is product of the digits of k.

1, 21, 6617, 12131, 12441, 114917, 121221, 124281, 125121, 145581, 172631, 182121, 191213, 211551, 221211, 221421, 241213, 293143, 421531, 421821

Offset: 1

Author

Farideh Firoozbakht, May 29 2010

Keywords

• base
• more
• nonn

Comments

All terms are odd. Large numbers corresponding to some terms are probable

prime. There is no further term up to 27500.

254597 < a(18) <= 293143. a(19) <= 421531. a(20) <= 421821. - Donovan Johnson, Aug 09 2010

Examples

			21^(2*1)+(2*1) is prime so 21 is a term.
		

Crossrefs

Cf. A178328, A099227.

Programs

Mathematica

Do[p=Apply[Times, IntegerDigits[n]]; If[PrimeQ[n^p+p], Print[n]],
{n, 1, 27501, 2}]

Extensions

No more terms less than 56600. - Robert G. Wilson v, Jul 27 2010

a(6)-a(17) from Donovan Johnson, Aug 09 2010

a(18)-a(20) from Michael S. Branicky, Jun 23 2023