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A122853 Numbers n such that (3^n + 5^n)/8 = A074606(n)/8 is a prime. 31
3, 5, 7, 17, 19, 109, 509, 661, 709, 1231, 12889, 13043, 26723, 43963, 44789 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

Corresponding primes of the form (3^n + 5^n)/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

Table of n, a(n) for n=1..15.

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

Cf. A074606, A081186, A121824, A121877, A005058, A005059, A121938, A109347, A079773.

Sequence in context: A062547 A125739 A219461 * A137258 A053341 A086086

Adjacent sequences:  A122850 A122851 A122852 * A122854 A122855 A122856

KEYWORD

more,nonn

AUTHOR

Alexander Adamchuk, Sep 14 2006

EXTENSIONS

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

STATUS

approved

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Last modified February 21 03:59 EST 2019. Contains 320364 sequences. (Running on oeis4.)