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

Author

N. J. A. Sloane, Henri Lifchitz

Keywords

• nonn

Links

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

Crossrefs

Cf. A013919, A013920, A053767.

Programs

Mathematica

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

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

Formula

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

Extensions

More terms from David W. Wilson

Name edited by Michel Marcus, Nov 25 2022