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A062198 Sum of first n semiprimes. 11
4, 10, 19, 29, 43, 58, 79, 101, 126, 152, 185, 219, 254, 292, 331, 377, 426, 477, 532, 589, 647, 709, 774, 843, 917, 994, 1076, 1161, 1247, 1334, 1425, 1518, 1612, 1707, 1813, 1924, 2039, 2157, 2276, 2397, 2519, 2642, 2771, 2904, 3038, 3179, 3321, 3464 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Elements in this sequence can themselves be semiprimes. a(1) = 4 = 2^2. a(2) = 10 = 2 * 5. a(6) = 58 = 2 * 29. a(11) = 185 = 5 * 37. a(12) = 219 = 3 * 73. a(13) = 254 = 2 * 127. a(16) = 377 = 13 * 29. a(20) = 589 = 19 * 31. Etc. 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} A001358(i). - R. J. Mathar, Sep 14 2012

EXAMPLE

a(4)=29 because sum of first 4 semiprimes i.e. 4+6+9+10 is 29.

MATHEMATICA

Accumulate[Select[Range[200], PrimeOmega[#]==2&]] (* Harvey P. Dale, Jul 23 2014 *)

PROG

(PARI) is_A062198(N)={ my(n=0); while(N>0, while(bigomega(n++)!=2, ); N-=n); !N}  \\ - M. F. Hasler, Sep 23 2012

(PARI) A062198(n, list)={my(s=0, N=0); until(!n--, until(bigomega(N++)==2, ); s+=N; list & print1(s", ")); s}  \\ - M. F. Hasler, Sep 23 2012

CROSSREFS

Sequence in context: A145731 A162958 A029714 * A050858 A173248 A267882

Adjacent sequences:  A062195 A062196 A062197 * A062199 A062200 A062201

KEYWORD

easy,nonn

AUTHOR

Shyam Sunder Gupta, Aug 24 2003

STATUS

approved

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Last modified July 23 22:27 EDT 2017. Contains 289716 sequences.