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

1,1

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.

Links

Table of n, a(n) for n=1..57.

Example

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

Mathematica

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

Prog

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

Crossrefs

Cf. A001222, A159919.

Sequence in context: A374253 A351291 A374254 * A059408 A164455 A164504

Adjacent sequences: A336260 A336261 A336262 * A336264 A336265 A336266

Keyword

nonn,easy

Author

Davide Rotondo, Jul 15 2020

Extensions

More terms from David A. Corneth, Jul 15 2020

Status

approved