A108633 Nonsquare semiprimes with semiprime sum of factors.

14, 21, 26, 33, 38, 46, 57, 62, 69, 74, 85, 93, 94, 106, 129, 133, 134, 145, 166, 177, 178, 205, 213, 217, 218, 226, 237, 249, 253, 254, 262, 265, 278, 309, 314, 334, 362, 393, 398, 417, 422, 445, 466, 469, 489, 493, 502, 505, 514, 517, 526, 553, 565, 573, 586

Offset

1,1

Comments

Squares of primes are not included. - Zak Seidov, Sep 14 2018

Links

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

Example

21 = 3*7 and 3 + 7 = 10 = 2*5.

Mathematica

Select[Range[800], Plus@@Last/@FactorInteger[ # ]==Plus@@Last/@FactorInteger[(Plus@@First/@FactorInteger[ # ])]==2&]

Prog

(PARI) is(n) = if(bigomega(n)!=2, return(0), my(f=factor(n)[, 1]~); #f==2 && bigomega(sum(i=1, #f, f[i]))==2) \\ Felix Fröhlich, Sep 17 2018

Crossrefs

Cf. A001358 (semiprimes), A006881 (squarefree semiprimes).

Sequence in context: A324073 A006614 A039832 * A110478 A125967 A284808

Adjacent sequences: A108630 A108631 A108632 * A108634 A108635 A108636

Keyword

nonn

Author

Zak Seidov, Jun 14 2005

Extensions

Name clarified by David A. Corneth, Sep 17 2018

Status

approved