A013921 Composite numbers that are equal to the sum of the first k composites for some k.

4, 10, 18, 27, 49, 63, 78, 94, 112, 132, 153, 175, 224, 250, 305, 335, 400, 434, 469, 505, 543, 582, 622, 664, 708, 753, 799, 847, 896, 946, 1158, 1214, 1271, 1329, 1389, 1514, 1578, 1643, 1846, 1916, 1988, 2062, 2290, 2368, 2448, 2529, 2611, 2695, 2780, 2866

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..10000

Formula

a(n) = A053767(A013919(n)). [Found by LODA miner] - Christian Krause, Nov 24 2022

Mathematica

Module[{nn=100, comps}, comps=Complement[Range[4, nn], Prime[ Range[ PrimePi[ nn]]]]; Select[Accumulate[comps], !PrimeQ[#]&]] (* Harvey P. Dale, May 21 2014 *)

Prog

(PARI) isok(c) = if ((c>1) && !isprime(c), my(s=0); forcomposite(x=1, oo, s+=x; if (s == c, return(1)); if (s > c, return(0)))); \\ Michel Marcus, Nov 25 2022

Crossrefs

Cf. A013919, A013920, A053767.

Sequence in context: A172484 A009876 A161958 * A217748 A028552 A009877

Adjacent sequences: A013918 A013919 A013920 * A013922 A013923 A013924

Keyword

nonn

Author

N. J. A. Sloane, Henri Lifchitz

Extensions

More terms from David W. Wilson

Name edited by Michel Marcus, Nov 25 2022

Status

approved