A175509 a(n) = ((2*n)-th semiprime) minus 2*(n-th semiprime).

-2, -2, -3, 2, -2, 4, -4, 2, 1, 5, -4, 1, 7, 9, 9, 1, -3, 9, 8, 7, 7, 9, 11, 5, -2, 4, -3, -1, 6, 11, 12, 16, 17, 19, 2, -5, -11, -10, -1, 7, 10, 16, 9, 12, 21, 13, 15, 16, 15, 22, 11, 10, 11, 13, 9, 17, 7, 9, 11, 12, 17, 6, -4, 3, 7, 7, 15, 27, 21, 25, 28, 35, 37, 43, 43, 41, 31, 31, 20

Offset: 1

Author

Juri-Stepan Gerasimov, Jun 02 2010

Keywords

• sign

Examples

			a(1) = -2 because ((2*1)-th semiprime) - 2*(1st semiprime) = 6 - 2*4 = -2.
		

Crossrefs

Cf. A066066.

Formula

a(n) = A099981(n) - A075818(n).

Extensions

Entries checked by R. J. Mathar, Aug 12 2010