A086062 Sum of first n 3-almost primes.

8, 20, 38, 58, 85, 113, 143, 185, 229, 274, 324, 376, 439, 505, 573, 643, 718, 794, 872, 964, 1062, 1161, 1263, 1368, 1478, 1592, 1708, 1825, 1949, 2074, 2204, 2342, 2489, 2637, 2790, 2944, 3108, 3273, 3443, 3614, 3786, 3960, 4135, 4317, 4503, 4691, 4881

Offset

1,1

Comments

Elements in this sequence can themselves be 3-almost primes. a(1) = 8 = 2^3. a(2) = 20 = 2^2 * 5. a(20) = 964 = 2^2 * 241. a(28) = 1825 = 5^2 * 73. a(30) = 2074 = 2 * 17 * 61. a(34) = 2637 = 3^2 * 293. a(40) = 3614 = 2 * 13 * 139. a(41) = 3786 = 2 * 3 * 631. a(45) = 4503 = 3 * 19 * 79. Does this happen infinitely often? - Jonathan Vos Post, Dec 11 2004

Links

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

Formula

a(n) = sum_{i=1..n} A014612(i). - R. J. Mathar, Sep 14 2012

Example

a(2)=20 because sum of first two 3-almost primes i.e. 8+12 is 20.

Mathematica

Accumulate[Select[Range[500], PrimeOmega[#]==3&]] (* Harvey P. Dale, Jan 17 2014 *)

Crossrefs

Sequence in context: A272805 A073607 A351967 * A006416 A375717 A273069

Adjacent sequences: A086059 A086060 A086061 * A086063 A086064 A086065

Keyword

easy,nonn

Author

Shyam Sunder Gupta, Aug 24 2003

Status

approved