A176629 a(n) = n-th semiprime - (-1)^(n-th semiprime).

3, 5, 10, 9, 13, 16, 22, 21, 26, 25, 34, 33, 36, 37, 40, 45, 50, 52, 56, 58, 57, 61, 66, 70, 73, 78, 81, 86, 85, 88, 92, 94, 93, 96, 105, 112, 116, 117, 120, 122, 121, 124, 130, 134, 133, 142, 141, 144, 146, 145, 156, 157, 160, 162, 165, 170, 178, 177, 184, 186, 188

Offset

1,1

Links

Table of n, a(n) for n=1..61.

Formula

a(n) = A001358(n) - (-1)^A001358(n).

Example

a(1)=3 because (1st semiprime) - (-1)^(1st semiprime) = 4 - 1 = 3.

Mathematica

#-(-1)^#&/@Select[Range[200], PrimeOmega[#]==2&] (* Harvey P. Dale, Nov 08 2012 *)

Crossrefs

Sequence in context: A332359 A328070 A286592 * A069193 A078430 A345892

Adjacent sequences: A176626 A176627 A176628 * A176630 A176631 A176632

Keyword

nonn

Author

Juri-Stepan Gerasimov, Apr 22 2010

Extensions

Entries checked by R. J. Mathar, Apr 27 2010

Status

approved