A122853 - OEIS

A122853

Numbers k such that (3^k + 5^k)/8 = A074606(k)/8 is a prime.

3, 5, 7, 17, 19, 109, 509, 661, 709, 1231, 12889, 13043, 26723, 43963, 44789

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OFFSET

1,1

COMMENTS

(3^k + 5^k)/8 = A074606(k)/8 = A081186(k)/4.

Corresponding primes of the form (3^k + 5^k)/2^3 are listed in {A121938(n)} = {A079773(a(n))} = {19, 421, 10039, 95383574161, 2384331073699, ...}.

No other terms less than 100000. - Robert Price, Apr 28 2012

LINKS

MATHEMATICA

Do[f=5^n+3^n; If[PrimeQ[f/2^3], Print[{n, f/2^3}]], {n, 1, 1231}]

PROG

(PARI) select(n->isprime((3^n + 5^n)/8), vector(2000, i, i)) \\ Charles R Greathouse IV, Feb 13 2011

CROSSREFS

KEYWORD

nonn,more

AUTHOR

EXTENSIONS

a(11)-a(15) from Robert Price, Apr 28 2012

STATUS

approved