A241264 Numbers k such that 2*k^2 + 2*k - 41 is not a prime.

4, 13, 20, 24, 26, 30, 31, 32, 35, 36, 37, 38, 40, 41, 43, 47, 49, 51, 54, 55, 60, 62, 63, 64, 67, 70, 71, 72, 73, 75, 76, 78, 79, 81, 82, 84, 85, 88, 89, 92, 94, 97, 98, 100, 102, 105, 108, 109, 111, 112, 113, 114, 115, 117, 118, 119, 120, 122, 123, 124, 125

Offset: 1

Author

Vincenzo Librandi, Apr 20 2014

Keywords

• nonn
• easy

Examples

			13 is in this sequence because 2*13^2 + 2*13 - 41 = 323 = 17*19.
		

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..5000

Crossrefs

Complement of A155771.

Programs

Magma

[n: n in [1..150] | not IsPrime(2*n^2+2*n-41)];

Mathematica

Select[Range[4, 200], ! PrimeQ[2 #^2 + 2 # - 41] &]