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A187367 Least odd number k such that (k*2^n-1)*k*2^n - 1 is prime. 5
3, 1, 5, 1, 1, 3, 5, 11, 1, 1, 19, 15, 13, 9, 35, 15, 5, 1, 35, 29, 31, 29, 13, 29, 27, 3, 27, 25, 31, 55, 19, 5, 77, 19, 57, 19, 33, 1, 17, 9, 27, 9, 29, 5, 1, 5, 35, 7, 73, 1, 183, 61, 31, 33, 9, 11, 1, 29, 215, 139, 33, 15, 35, 41, 37, 121, 63, 15, 23, 25 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

As N increases, it appears that (sum_{k=1..N} a(k)) / (sum_{k=1..N} k) tends to 0.8.

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, 70}]

CROSSREFS

Cf. A187368, A187369, A187370, A187371.

Sequence in context: A344592 A176801 A339903 * A307410 A305444 A002945

Adjacent sequences:  A187364 A187365 A187366 * A187368 A187369 A187370

KEYWORD

nonn

AUTHOR

Pierre CAMI, Mar 09 2011

STATUS

approved

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Last modified August 1 15:18 EDT 2021. Contains 346393 sequences. (Running on oeis4.)