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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
OFFSET
1,3
LINKS
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 A334085 A249831
KEYWORD
nonn
AUTHOR
Michel Lagneau, Aug 05 2011
STATUS
approved