A109310 Numbers n such that difference between n-th and (n+1)-st semiprimes is a semiprime (sp).

4, 6, 18, 21, 23, 30, 36, 42, 43, 50, 68, 76, 78, 80, 87, 88, 91, 98, 108, 111, 116, 117, 118, 120, 127, 128, 134, 138, 141, 150, 151, 152, 153, 156, 164, 168, 171, 179, 185, 186, 192, 195, 196, 204, 212, 215, 216, 226, 232, 236, 237, 244, 245, 250, 255, 266

Offset: 1

Author

Zak Seidov, Jun 27 2005

Keywords

• nonn

Examples

			4 is ok because sp(4)=10, sp(5)=14, 14-10=sp(1), sp(n)=A001358(n)=n-th semiprime.
		

Crossrefs

Cf. A001358 = Semiprimes, A092191 = numbers n such that sum of n-th and (n+1)-st semiprimes is a semiprime.

Programs

PARI

lista(nn) = {vec = vector(nn, i, i); sp = select(i->(bigomega(i)==2), vec); for (i = 1, #sp-1, if (bigomega(sp[i+1]-sp[i]) == 2, print1(i, ", ")););} \\ Michel Marcus, Oct 06 2013