A102630 - OEIS

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A102630

Numbers n such that no positive number of the form prime(n)-2^k is prime.

1, 2, 31, 35, 54, 67, 68, 74, 97, 109, 126, 134, 140, 151, 155, 165, 168, 171, 181, 205, 244, 251, 256, 260, 274, 275, 276, 285, 298, 328, 330, 341, 352, 368, 376, 389, 405, 413, 417, 421, 430, 444, 447, 450, 451, 463, 471, 481, 495, 509, 510, 516, 522, 526

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OFFSET

1,2

COMMENTS

Large primes tested by Primo.

LINKS

Table of n, a(n) for n=1..54.

Lei Zhou, Between 2^n and primes.

EXAMPLE

Prime(1)=2, 2-2^0=1, not prime.

Prime(31)=127, 127-2^0 through 127-2^6 are nonprime.

MATHEMATICA

fQ[n_] := Block[{k = Floor[ Log[2, Prime[n]]], p = Prime[n]}, While[k > -1 && !PrimeQ[p - 2^k], k-- ]; If[k > 0, True, False]]; Select[ Range[ 536], !fQ[ # ] &] (* Robert G. Wilson v, Jan 24 2005 *)

CROSSREFS

Cf. A094076, A102631-A102633.

Sequence in context: A020896 A042153 A267207 * A264783 A215031 A120638

Adjacent sequences: A102627 A102628 A102629 * A102631 A102632 A102633

KEYWORD

nonn

AUTHOR

Lei Zhou, Jan 20 2005

EXTENSIONS

More terms from Robert G. Wilson v, Jan 24 2005

STATUS

approved