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A058934 Numbers n such that 2*5^n + 1 is prime. 1
0, 1, 3, 13, 45, 105, 159, 297, 1443, 2977, 3699, 11709, 12357, 43165, 121995 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

a(n) is odd for n>0. Next term > 17200. - Julián Aguirre, Apr 22 2011

a(16) > 2*10^5. - Robert Price, Mar 14 2015

LINKS

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

EXAMPLE

a(3)=13 and 1+2*5^13=2441406251 is prime.

MATHEMATICA

Select[Range[0, 16000], PrimeQ[2*5^#+1]&] (* Julián Aguirre, Apr 22 2011 *)

PROG

(Sage)

for n in range(16000):

...if is_prime(2*5^n+1):

...print(n)

## Julián Aguirre, Apr 22 2011

(PARI) is(n)=ispseudoprime(2*5^n+1) \\ Charles R Greathouse IV, Jun 12 2017

CROSSREFS

Cf. A003306 (2*3^n + 1 is prime), A120375 (2*5^n-1 is prime).

Sequence in context: A095863 A136520 A212416 * A141088 A187915 A115128

Adjacent sequences:  A058931 A058932 A058933 * A058935 A058936 A058937

KEYWORD

nonn

AUTHOR

Labos Elemer, Jan 12 2001

EXTENSIONS

Edited by Joerg Arndt, Apr 22 2011

Terms 1443,...,12357 from Julián Aguirre, Apr 22 2011

a(14)-a(15) from Robert Price, Mar 14 2015

STATUS

approved

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Last modified April 18 13:05 EDT 2019. Contains 322209 sequences. (Running on oeis4.)