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A013919 Numbers n such that sum of first n composites is composite. 5
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 (list; graph; refs; listen; history; text; internal format)
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 A004776

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

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Last modified August 13 06:22 EDT 2020. Contains 336442 sequences. (Running on oeis4.)