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

1,2

LINKS

Table of n, a(n) for n=1..20.

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: A342715 A050079 A314313 * A066980 A055052 A314314

Adjacent sequences:  A339918 A339919 A339920 * A339922 A339923 A339924

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

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Last modified September 26 14:45 EDT 2021. Contains 347668 sequences. (Running on oeis4.)