A336263 - OEIS

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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

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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 *)