A187369 - OEIS

A187369

Least odd number k such that (k*2^n+1)*k*2^n - 1 is prime.

1, 1, 1, 1, 3, 1, 5, 19, 9, 1, 11, 13, 13, 11, 21, 1, 15, 5, 41, 41, 39, 17, 7, 1, 25, 1, 27, 51, 13, 11, 47, 39, 37, 39, 1, 45, 15, 5, 23, 13, 59, 5, 47, 175, 35, 11, 53, 15, 19, 131, 41, 1, 45, 17, 1, 53, 83, 49, 85, 159, 123, 69, 23, 29, 23, 207, 37, 19, 37, 39, 91, 13, 57

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OFFSET

1,5

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, 100}]

CROSSREFS

Cf. A187367, A187368, A187370, A187371.

Sequence in context: A368340 A338172 A104053 * A039512 A140825 A265981

Adjacent sequences: A187366 A187367 A187368 * A187370 A187371 A187372

KEYWORD

nonn

AUTHOR

Pierre CAMI, Mar 09 2011

STATUS

approved