A013919 Numbers n such that sum of first n composites is composite.

1, 2, 3, 4, 6, 7, 8, 9, 10, 11, 12, 13, 15, 16, 18, 19, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 38, 39, 40, 41, 42, 44, 45, 46, 49, 50, 51, 52, 55, 56, 57, 58, 59, 60, 61, 62, 65, 66, 67, 69, 70, 71, 72, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 87, 88, 89, 90, 91, 92, 93

Offset

1,2

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Mathematica

f[ n_Integer ] := Block[ {k = n + PrimePi[ n ] + 1}, While[ k - PrimePi[ k ] - 1 != n, k++ ]; k ]; s = 0; Do[ s = s + f[ n ]; If[ ! PrimeQ[ s ], Print[ n ] ], {n, 1, 100} ]
With[{comps=Rest[Select[Range[150], !PrimeQ[#]&]]}, Rest[Flatten[ Position[ Accumulate[ comps], _?(!PrimeQ[#]&)]]]] (* Harvey P. Dale, Oct 16 2013 *)

Crossrefs

Cf. A013920, A013921.

Sequence in context: A323733 A003247 A076216 * A101771 A035058 A350757

Adjacent sequences: A013916 A013917 A013918 * A013920 A013921 A013922

Keyword

nonn

Author

N. J. A. Sloane, Henri Lifchitz

Extensions

More terms from David W. Wilson

Status

approved