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A193807 Smallest positive integer k such that n*k^2 + 1 is a prime. 6
1, 1, 2, 1, 6, 1, 2, 3, 2, 1, 6, 1, 2, 3, 2, 1, 6, 1, 8, 3, 4, 1, 6, 2, 2, 6, 2, 1, 12, 1, 6, 6, 8, 2, 24, 1, 2, 9, 2, 1, 30, 1, 2, 3, 2, 1, 6, 2, 2, 6, 10, 1, 24, 3, 4, 6, 2, 1, 30, 1, 4, 9, 4, 2, 6, 1, 2, 3, 2, 1, 6, 1, 2, 12, 4, 4, 36, 1, 2, 9, 4, 1, 12 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

EXAMPLE

a(5) = 6 because 5*6^2 + 1 = 181 is prime.

MATHEMATICA

Table[k = 0; While[!PrimeQ[n*k^2 + 1], k++]; k, {n, 110}]

PROG

(PARI) a(n) = my(k=1); while (!isprime(n*k^2 + 1), k++); k; \\ Michel Marcus, Aug 19 2019

CROSSREFS

Sequence in context: A082388 A178254 A085099 * A225766 A249831 A304527

Adjacent sequences:  A193804 A193805 A193806 * A193808 A193809 A193810

KEYWORD

nonn

AUTHOR

Michel Lagneau, Aug 05 2011

STATUS

approved

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Last modified December 12 20:12 EST 2019. Contains 329961 sequences. (Running on oeis4.)