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A301634 Numbers k such that 2^k + 2*k + 1 is prime. 3
0, 1, 5, 13, 65, 85, 229, 2005, 3875, 3919, 5417, 8819, 11899, 16668, 19445, 28242, 37918, 40594 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Next term, if it exists, is greater than 50000. Terms up to 229 correspond to provable primes. The terms greater than or equal to 2005 correspond to probable primes. - Jon E. Schoenfield and Vaclav Kotesovec, Mar 27 2018

LINKS

Table of n, a(n) for n=1..18.

MAPLE

a:=k->`if`(isprime(2^k+2*k+1), k, NULL): seq(a(k), k=0..6000); # Muniru A Asiru, Mar 25 2018

MATHEMATICA

Flatten[{0, Select[Range[5000], PrimeQ[2^# + 2*# + 1] &]}] (* Vaclav Kotesovec, Mar 25 2018 *)

PROG

(PARI) for(n=0, 500, if(isprime(2^n+2*n+1), print1(n", ")))

CROSSREFS

A163115 gives the primes.

Numbers k such that b^k + b*k + 1 is prime: this sequence (b=2), A171058 (b=3), A301635 (b=5).

Cf. A176691.

Sequence in context: A149572 A149573 A149574 * A309167 A272069 A018678

Adjacent sequences:  A301631 A301632 A301633 * A301635 A301636 A301637

KEYWORD

nonn,more,hard

AUTHOR

Seiichi Manyama, Mar 25 2018

EXTENSIONS

a(9)-a(15) from Vaclav Kotesovec, Mar 25 2018

a(16)-a(18) from Jon E. Schoenfield, Mar 26 2018

STATUS

approved

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Last modified December 8 02:30 EST 2019. Contains 329850 sequences. (Running on oeis4.)