A032487 - OEIS

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A032487

Numbers k such that 221*2^k+1 is prime.

1, 7, 9, 13, 21, 67, 77, 81, 89, 101, 117, 131, 161, 181, 229, 641, 753, 789, 911, 1351, 1461, 1819, 2391, 2951, 4381, 4531, 5633, 6577, 6671, 8521, 10059, 10453, 13571, 15427, 15541, 15969, 16601, 49013, 69831, 118213, 134709, 135281, 180973, 271961, 324567

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

Jeppe Stig Nielsen, Table of n, a(n) for n = 1..52

Ray Ballinger and Wilfrid Keller, List of primes k.2^n + 1 for k < 300

Wilfrid Keller, List of primes k.2^n - 1 for k < 300

Index entries for sequences of n such that k*2^n-1 (or k*2^n+1) is prime

MATHEMATICA

Select[Range[1000], PrimeQ[221*2^# + 1] & ] (* Robert Price, Dec 19 2018 *)

PROG

(PARI) is(n)=ispseudoprime(221*2^n+1) \\ Charles R Greathouse IV, Jun 13 2017