A243436 Numbers n such that n^2-n-1 is semiprime.

8, 13, 15, 18, 19, 23, 24, 26, 28, 30, 33, 34, 35, 38, 41, 44, 50, 52, 58, 59, 62, 64, 68, 70, 72, 73, 74, 75, 76, 78, 79, 80, 82, 83, 88, 89, 91, 92, 96, 98, 99, 100, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 117, 119, 120, 122, 123, 124, 125, 128, 130

Offset: 1

Author

K. D. Bajpai, Jun 06 2014

Keywords

• nonn

Examples

			13 is in the sequence because 13^2 - 13 - 1 = 155 = 5 * 31 is semiprime.
18 is in the sequence because 18^2 - 18 - 1 = 305 = 5 * 61 is semiprime.
		

Links

• K. D. Bajpai, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A001358, A165900.

Programs

Maple

with(numtheory):A243436 := proc() if bigomega(n^2-n-1)=2 then RETURN (n); fi; end: seq(A243436 (), n=1..200);

Mathematica

c = 0; Do[If[PrimeOmega[n^2-n-1] == 2, c++; Print[c," ",n]], {n,1,30000}];
Select[Range[200],PrimeOmega[#^2-#-1]==2&] (* Harvey P. Dale, Sep 21 2016 *)