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A187368 Least odd number k such that (k*2^n-1)*k*2^n + 1 is prime. 5
1, 1, 9, 1, 9, 7, 3, 9, 39, 31, 5, 25, 3, 15, 27, 9, 39, 7, 3, 19, 9, 45, 29, 7, 11, 15, 51, 79, 23, 67, 35, 1, 21, 85, 63, 21, 29, 39, 9, 9, 53, 13, 29, 39, 69, 115, 5, 9, 3, 51, 41, 9, 9, 109, 15, 15, 63, 31, 95, 195, 81, 15, 207, 63, 63, 43, 105, 57, 141, 163, 53 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

As N increases, it appears that (sum_{k=1..N} a(k)) / (sum_{k=1..N} k) tends to 1.25

LINKS

Pierre CAMI, Table of n, a(n) for n = 1..4000

MATHEMATICA

Table[k = 1; While[! PrimeQ[(k*2^n - 1)*k*2^n + 1], k = k + 2]; k, {n, 100}]

CROSSREFS

Cf. A187367, A187369, A187370, A187371.

Sequence in context: A197724 A176518 A154697 * A193670 A309614 A154220

Adjacent sequences:  A187365 A187366 A187367 * A187369 A187370 A187371

KEYWORD

nonn

AUTHOR

Pierre CAMI, Mar 09 2011

STATUS

approved

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Last modified July 29 17:41 EDT 2021. Contains 346346 sequences. (Running on oeis4.)