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A178327 Numbers n such that n^p+p is prime, where p is product of the digits of n. 1
1, 21, 6617, 12131, 12441, 114917, 121221, 124281, 125121, 145581, 172631, 182121, 191213, 211551, 221211, 221421, 241213 (list; graph; refs; listen; history; text; internal format)
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. [From Donovan Johnson, Aug 09 2010]

LINKS

Table of n, a(n) for n=1..17.

EXAMPLE

21^(2*1)+(2*1) is prime so 21 is in the sequence.

MATHEMATICA

Do[p=Apply[Times, IntegerDigits[n]]; If[PrimeQ[n^p+p], Print[n]],

{n, 1, 27501, 2}]

CROSSREFS

Cf. A178328.

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. [From Robert G. Wilson v, Jul 27 2010]

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

STATUS

approved

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Last modified December 9 07:21 EST 2021. Contains 349627 sequences. (Running on oeis4.)