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

1,2

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

Links

Table of n, a(n) for n=1..20.

Example

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

Mathematica

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

Crossrefs

Cf. A178328, A099227.

Sequence in context: A220552 A275053 A028451 * A231906 A250063 A307931

Adjacent sequences: A178324 A178325 A178326 * A178328 A178329 A178330

Keyword

base,more,nonn

Author

Farideh Firoozbakht, May 29 2010

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

Status

approved