A131284 Numbers n such that difference between prime factors of n-th semiprime is n.

5, 80, 86, 613668, 6384425704

Offset: 1

Author

Zak Seidov, Sep 25 2007

Keywords

• more
• nonn

Comments

The 6384425704th semiprime is 44690979977 = 7*6384425711. 6384425711 - 7 = 6384425704. - Donovan Johnson, Jul 11 2010

Examples

			sp(5) = 14 = 2*7 and 7 - 2 = 5, sp(80) = 249 = 3*83 and 83 - 3 = 80, sp(86) = 267 = 3*89 and 89 - 3 = 86; sp(n) = n-th semiprime.
		

Crossrefs

Cf. A064910, A084126, A084127, A109313.

Programs

PARI

{ n=0; j=1; /* n=3068365-1; j=613668;*/
while( l=(j\10^4+1)*10^4, until( l < j++, until(bigomega(n+=1)==2,);
if(2!=#f=factor(n)[,1],next); if(j==f[2]-f[1],print("\n",[j,n,f])));
print1(j-1,":"n", "))} \\ M. F. Hasler, Sep 28 2007

Extensions

a(4) = 613668 (p=5, q=613673) from M. F. Hasler, Sep 28 2007

a(5) from Donovan Johnson, Jul 11 2010