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

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

Cf. A006882, A001358, A115651, A115652, A115653.

Sequence in context: A253106 A320969 A113433 * A362910 A036326 A078972

Adjacent sequences: A115651 A115652 A115653 * A115655 A115656 A115657

Keyword

nonn

Author

Giovanni Resta, Jan 28 2006

Status

approved