A161538 - OEIS

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A161538

Numbers n such that composite (n) + n is a prime, where composite (n) denotes the n-th composite number.

1, 3, 4, 8, 11, 27, 29, 40, 44, 45, 47, 57, 58, 66, 69, 71, 83, 84, 90, 100, 103, 108, 111, 116, 117, 127, 133, 135, 136, 144, 147, 151, 153, 156, 160, 163, 176, 179, 197, 201, 211, 214, 216, 221, 239, 242, 251, 252, 255, 260, 263, 269, 272, 274, 275, 280, 287

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OFFSET

1,2

COMMENTS

8 is in the list because composite(8) + 8 = 15 + 8 = 23 is prime.

27 is in the list because composite(27) + 27 = 40 + 27 = 67 is prime.

LINKS

Table of n, a(n) for n=1..57.

MATHEMATICA

nn=400; With[{cnos=Rest[Complement[Range[nn], Prime[Range[PrimePi[nn]]]]]}, Transpose[Select[Thread[{cnos, Range[Length[cnos]]}], PrimeQ[Total[#]]&]][[2]]] (* Harvey P. Dale, Mar 24 2011 *)

CROSSREFS

Cf. A002808.

Complement of A161539.

Sequence in context: A126873 A263768 A050316 * A319980 A170885 A080646

Adjacent sequences: A161535 A161536 A161537 * A161539 A161540 A161541

KEYWORD

nonn

AUTHOR

Claudio Meller, Jun 13 2009

STATUS

approved