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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). 1
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 (list; graph; refs; listen; history; text; internal format)
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: A158998 A122559 A132131 * 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

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Last modified October 17 17:21 EDT 2021. Contains 348065 sequences. (Running on oeis4.)