A161539 Numbers n such that composite (n) + n is a composite, where composite (n) denotes the n-th composite number.

2, 5, 6, 7, 9, 10, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 28, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 41, 42, 43, 46, 48, 49, 50, 51, 52, 53, 54, 55, 56, 59, 60, 61, 62, 63, 64, 65, 67, 68, 70, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 85, 86, 87, 88, 89

Offset

1,1

Comments

2 is in the list because composite(2)+2 =6+2 = 8 and 8 is composite.

5 is in the list because composite(5)+5 =10+5 = 15 and 15 is composite.

Links

Table of n, a(n) for n=1..71.

Mathematica

With[{comps=Complement[Range[2, 250], Prime[Range[PrimePi[250]]]]}, Transpose[Select[Thread[{Range[Length[comps]], comps}], !PrimeQ[ Total[#]]&]][[1]]] (* Harvey P. Dale, Dec 02 2011 *)

Crossrefs

Cf. A002808.

Complement of A161538.

Sequence in context: A303437 A187578 A193260 * A177859 A047580 A153384

Adjacent sequences: A161536 A161537 A161538 * A161540 A161541 A161542

Keyword

nonn

Author

Claudio Meller, Jun 13 2009

Status

approved