OFFSET

1,1

COMMENTS

5^n + n is composite for all n < 1000. - Pete L. Clark ( Department of Mathematics University of Georgia).

5^7954 + 7954 has been found to be prime by a computer (see Links).

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..182

5^n+n is never prime? 5^n+n is never prime?

Mersenneforum.org discussion, 5^7954 + 7954 has been found to be prime by a computer

FORMULA

EXAMPLE

a(5) = 3 because 5^5 + 5 = 2*5*313 has 3 prime factors.

MAPLE

with(numtheory):for n from 1 to 100 do:x:=5^n + n: y:=nops(factorset(x)):printf(`%d, `, y):od:

MATHEMATICA

PrimeNu/@Table[5^n+n, {n, 20}] (* Harvey P. Dale, Feb 17 2013 *)

PROG

(PARI) a(n)=omega(5^n+n) \\ Charles R Greathouse IV, Aug 27 2014

(Magma) [#PrimeDivisors(5^n+n): n in [1..107]]; // Marius A. Burtea, Feb 19 2020

CROSSREFS

KEYWORD

nonn

AUTHOR

Michel Lagneau, Jan 30 2011

EXTENSIONS

a(71)-a(87) from Amiram Eldar, Feb 19 2020

STATUS

approved