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

1,1

Links

Table of n, a(n) for n=1..56.

Example

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

Prog

(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

Crossrefs

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

Sequence in context: A062046 A102020 A125133 * A219190 A337617 A120391

Adjacent sequences: A109307 A109308 A109309 * A109311 A109312 A109313

Keyword

nonn

Author

Zak Seidov, Jun 27 2005

Status

approved