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A037039
Least k such that 4*n*k+1 is a prime.
0
1, 2, 1, 1, 2, 3, 1, 3, 1, 1, 2, 2, 1, 2, 1, 3, 2, 1, 3, 3, 4, 1, 3, 1, 1, 3, 1, 1, 2, 2, 3, 2, 3, 1, 2, 3, 1, 3, 1, 4, 5, 2, 1, 2, 1, 7, 5, 1, 1, 2, 2, 6, 5, 2, 3, 2, 1, 1, 3, 1, 3, 6, 3, 1, 2, 5, 1, 5, 1, 1, 2, 2, 1, 2, 2, 4, 2, 1, 1, 2, 4, 7, 3, 1, 3, 3, 1, 1, 3, 5, 3, 9, 1, 3, 2, 2, 1, 8, 1, 1, 2, 1, 3, 3, 1
OFFSET
1,2
EXAMPLE
a(5)=2 because for n=5: 4*5*2+1=41 is a prime.
PROG
(PARI) a(n) = my(k = 0); while (! isprime(4*n*k+1), k++); k; \\ Michel Marcus, Sep 28 2013
CROSSREFS
Cf. A016014.
Sequence in context: A097868 A025830 A083796 * A333856 A182972 A153452
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from Erich Friedman
STATUS
approved