A123754 Positive numbers of the form 4*n^2 - 1 which are not semiprimes.

3, 63, 99, 195, 255, 399, 483, 575, 675, 783, 1023, 1155, 1295, 1443, 1599, 1935, 2115, 2303, 2499, 2703, 2915, 3135, 3363, 3843, 4095, 4355, 4623, 4899, 5475, 5775, 6083, 6399, 6723, 7055, 7395, 7743, 8099, 8463, 8835, 9215, 9603, 9999, 10815

Offset: 1

Author

Roger L. Bagula, Nov 16 2006

Keywords

• nonn

Comments

Positive numbers of the form 4*n^2 - 1 which are semiprimes can be found in A037074.

Or, all positive products of the form A014076(i)*[A014076(i)+-2], duplicates removed. - R. J. Mathar, Aug 08 2007

Links

• G. C. Greubel, Table of n, a(n) for n = 1..5000

Crossrefs

Cf. A000466, A037074.

Programs

Mathematica

Select[4*(Range[54])^2-1, Not[PrimeQ[Sqrt[(#+ 1)]-1] && PrimeQ[Sqrt[(#+1)]+1]]&]
Select[4*Range[100]^2-1,PrimeOmega[#]!=2&] (* Harvey P. Dale, Jul 24 2016 *)

Formula

Equals ( A000466 - {-1} ) - A001358. - R. J. Mathar, Aug 08 2007

Extensions

Edited by N. J. A. Sloane, Aug 03 2007