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A115654

Semiprimes (A001358) which are the sum of distinct double factorials (A006882).

4, 6, 9, 10, 14, 15, 21, 25, 26, 49, 51, 57, 58, 62, 65, 69, 74, 77, 106, 111, 115, 118, 119, 121, 122, 123, 129, 133, 134, 155, 158, 159, 161, 166, 169, 177, 178, 386, 393, 394, 395, 398, 403, 407, 411, 413, 437, 445, 446, 447, 451, 453, 458, 489, 493, 497

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OFFSET

1,1

COMMENTS

Double factorials 0!! and 1!! are not considered distinct. Note that double factorial (n!!) is different from (n!)!.

LINKS

Table of n, a(n) for n=1..56.

EXAMPLE

384 = 2*19 = 8!!+2!!.

MATHEMATICA

Union[Select[Total/@Subsets[Range[10]!!, 10], PrimeOmega[#]==2&]] (* Harvey P. Dale, Aug 24 2012 *)

CROSSREFS