A115585 Semiprimes with a semiprime sum of factors.

4, 9, 14, 21, 25, 26, 33, 38, 46, 49, 57, 62, 69, 74, 85, 93, 94, 106, 121, 129, 133, 134, 145, 166, 169, 177, 178, 205, 213, 217, 218, 226, 237, 249, 253, 254, 262, 265, 278, 289, 309, 314, 334, 361, 362, 393, 398, 417, 422, 445, 466, 469, 489, 493, 502, 505

Offset

1,1

Links

Zak Seidov, Table of n, a(n) for n = 1..1000

Example

314 = 2*157 and 2 + 157 = 159 =3 * 53 (semiprime).

Mathematica

fQ[n_] := Plus @@ Last /@ FactorInteger@n == 2; Select[ Range@513, fQ@# && fQ[ Plus @@ Flatten[ Table[First@#, {Last@#}] & /@ FactorInteger@# ]] &] (* Robert G. Wilson v *)
Select[Range[600], PrimeOmega[#]==PrimeOmega[Total[Flatten[Table[#[[1]], {#[[2]]}]&/@FactorInteger[#]]]]==2&] (* Harvey P. Dale, Jan 22 2013 *)

Prog

(PARI) list(lim)=my(v=List()); forprime(p=2, sqrt(lim), forprime(q=p, lim\p, if(bigomega(p+q)==2, listput(v, p*q)))); vecsort(Vec(v)) \\ Charles R Greathouse IV, Sep 09 2012

Crossrefs

Cf. A001358, A068318.

Sequence in context: A347581 A348149 A023488 * A099980 A281314 A004630

Adjacent sequences: A115582 A115583 A115584 * A115586 A115587 A115588

Keyword

nonn

Author

Zak Seidov, Mar 09 2006

Extensions

More terms from Robert G. Wilson v, Apr 12 2006

Status

approved