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A180130 Smallest k such that k*2^n is a sum of two successive primes. 9
5, 4, 2, 1, 7, 4, 2, 1, 9, 15, 8, 4, 2, 1, 25, 19, 11, 12, 6, 3, 10, 5, 35, 33, 52, 26, 13, 28, 14, 7, 15, 38, 19, 45, 47, 26, 13, 43, 84, 42, 21, 39, 35, 18, 9, 46, 23, 43, 49, 104, 52, 26, 13, 48, 24, 12, 6, 3, 21, 36, 18, 9, 15, 15, 9, 42, 21, 23, 67, 62, 31, 64, 32, 16, 8, 4, 2, 1, 45 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

If a(n) == 0 (mod 2), then a(n+1) = a(n)/2.

Records: 5, 7, 9, 15, 25, 35, 52, 84, 104, 146, 284, 330, 645, 660, 1020, 1677, 1701, 1747, 2247, 2991, ..., .

Corresponding primes which are twin primes for n = 0, 1, 2, 3, 8, 17, 18, 19, 23, 43, 44, 64, 156, 189, 190, 210, 211, 212, 264, 265, 281, 282, 283, 388, 547, 725, 726, 727, ..., .

LINKS

Robert G. Wilson v, Table of n, a(n) for n = 0..1000

MATHEMATICA

f[n_] := Block[{k = 1, j = 2^n/2}, While[ h = k*j; PrimeQ@h || NextPrime[h, -1] + NextPrime@h != 2 h, k++ ]; k]; Array[f, 79, 0]

CROSSREFS

Cf. A180131, A180132, A180133, A180134, A179975, A180135, A180136, A180137, A180138.

Sequence in context: A201680 A109430 A085917 * A242600 A102593 A090462

Adjacent sequences:  A180127 A180128 A180129 * A180131 A180132 A180133

KEYWORD

base,nonn

AUTHOR

Zak Seidov & Robert G. Wilson v, Aug 15 2010

STATUS

approved

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Last modified September 2 14:44 EDT 2014. Contains 246361 sequences.