A336263 Numbers of the form k + s + 2*k*s where k is a positive integer and s is a Sundaram number (A159919).

13, 22, 31, 37, 40, 49, 52, 58, 62, 67, 73, 76, 82, 85, 87, 94, 97, 103, 112, 115, 121, 122, 127, 130, 136, 137, 139, 142, 148, 157, 162, 166, 171, 172, 175, 178, 181, 184, 187, 192, 193, 199, 202, 211, 212, 214, 217, 220, 227, 229, 232, 237, 238, 241, 247, 253, 256

Offset: 1

Author

Davide Rotondo, Jul 15 2020

Keywords

• nonn
• easy

Comments

Numbers k such that bigomega(2*k + 1) >= 3. - David A. Corneth, Jul 15 2020

If a term s in A159919 is not here, 2*s+1 is a semiprime.

Examples

			4 is a Sundaram number, therefore 1+4+2*4*1=13 is a term, and (13*2)+1=27 is not a semiprime.
		

Crossrefs

Cf. A001222, A159919.

Programs

Mathematica

Select[Range[2^8], PrimeOmega[2*# + 1] >= 3 &] (* Amiram Eldar, Jul 15 2020 *)

PARI

is(n) = bigomega(2*n + 1) >= 3 \\ David A. Corneth, Jul 15 2020

Extensions

More terms from David A. Corneth, Jul 15 2020