id:A128979 - OEIS Search Results

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Least exponent k such that p_n*(2^k) - 1 is prime.

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1, 1, 2, 1, 2, 3, 2, 1, 4, 4, 1, 1, 2, 7, 4, 2, 12, 3, 5, 2, 7, 1, 2, 4, 1, 10, 3, 10, 9, 8, 25, 2, 2, 1, 4, 5, 1, 3, 4, 2, 8, 3, 226, 3, 2, 1, 1, 3, 2, 1, 4, 4, 11, 6, 4, 2, 8, 1, 5, 2, 11, 2, 1, 26, 3, 6, 1, 1, 18, 3, 4, 4, 1, 7, 1, 2, 20, 5, 10, 3, 4, 7, 2, 3, 1, 6, 112, 9, 10, 7, 2, 12, 5, 46, 1, 2, 8 (list; graph; listen)

	OFFSET	`1,3`
	COMMENT	`Supposedly the difference to A101050 is that the k here are required to be strictly positive (nonzero positive). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Dec 13 2008]`
	LINKS	`Pierre CAMI and Robert G. Wilson v, Table of n, a(n) for n = 1..119.`
	MATHEMATICA	`f[n_] := Block[{k = 1, p = Prime@n}, While[ !PrimeQ[p*2^k - 1], k++ ]; k]; Array[f, 97]`
	CROSSREFS	`Cf. A000040, A126715.` `Sequence in context: A055095 A048685 A101050 this_sequence A115116 A141662 A088062` `Adjacent sequences: A128976 A128977 A128978 this_sequence A128980 A128981 A128982`
	KEYWORD	`nonn`
	AUTHOR	`Pierre CAMI (pierrecami(AT)tele2.fr) & Robert G. Wilson v (rgwv(AT)rgwv.com), Feb 16 2007`

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Last modified December 18 21:37 EST 2009. Contains 171024 sequences.

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