login
A339921
Numbers k such that 20^k + 3 is prime.
1
1, 5, 7, 13, 15, 18, 22, 61, 85, 208, 271, 898, 2142, 2856, 4392, 17171, 74886, 78901, 271951, 326600
OFFSET
1,2
EXAMPLE
1 is a term since 20^1 + 3 = 23 is a prime.
MATHEMATICA
Do[ If[ PrimeQ[ 20^n + 3], Print[n]], {n, 0, 100000}]
PROG
(PARI) is(n)=isprime(20^n + 3)
CROSSREFS
Cf. A339922.
Sequence in context: A050079 A372081 A314313 * A066980 A055052 A314314
KEYWORD
nonn,more
AUTHOR
Paul Bourdelais, Dec 23 2020
EXTENSIONS
a(19)-a(20) correspond to probable primes discovered by Paul Bourdelais, Jan 06 2021
STATUS
approved