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

Author

Zak Seidov, Jun 14 2005

Keywords

• nonn

Comments

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

Examples

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

Links

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

Crossrefs

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

Programs

Mathematica

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

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

Extensions

Name clarified by David A. Corneth, Sep 17 2018