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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

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OFFSET

1,1

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

FORMULA

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

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 *)

CROSSREFS

Cf. A000466, A037074.

Sequence in context: A333041 A323726 A087886 * A377733 A048354 A046181

Adjacent sequences: A123751 A123752 A123753 * A123755 A123756 A123757

KEYWORD

nonn

AUTHOR

Roger L. Bagula, Nov 16 2006

EXTENSIONS

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

STATUS

approved

URL: https://oeis.org/A123754

⇱ A123754 - OEIS