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A103961 Least k such that 2*n*k - 1 is a prime. 0
2, 1, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 4, 3, 1, 1, 2, 2, 1, 2, 1, 1, 3, 1, 3, 2, 1, 3, 3, 1, 1, 2, 2, 1, 2, 1, 1, 2, 3, 1, 2, 1, 3, 3, 1, 4, 3, 2, 1, 2, 1, 1, 2, 1, 1, 2, 1, 3, 3, 2, 4, 5, 2, 1, 3, 1, 3, 2, 1, 1, 2, 3, 7, 3, 1, 1, 2, 2, 1, 3, 4, 1, 2, 1, 3, 5, 1, 7, 8, 1, 1, 2, 3, 3, 2, 1, 1, 3, 1, 1, 5, 5, 3, 5, 2 (list; graph; refs; listen; history; internal format)
OFFSET

1,1

EXAMPLE

2*1*2-1=3, so a(1)=2;

2*5*2-1=19, so a(5)=2

MATHEMATICA

Do[k = 1; cp = n*k - 1; While[ ! PrimeQ[cp], k++; cp = n*k - 1]; Print[k], {n, 2, 400, 2}]

CROSSREFS

Cf. A016014.

Sequence in context: A198254 A106035 A105141 * A071891 A046072 A072273

Adjacent sequences:  A103958 A103959 A103960 * A103962 A103963 A103964

KEYWORD

easy,nonn

AUTHOR

Lei Zhou (lzhou5(AT)emory.edu), Feb 23 2005

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Last modified February 16 11:20 EST 2012. Contains 205906 sequences.