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A339480 Numbers of the form (k^2 - 2) / 2 where k - 1 and k + 1 are both odd composite numbers. 0
337, 577, 1249, 1567, 2047, 2887, 3697, 4231, 4417, 6727, 6961, 7199, 7441, 7687, 8977, 10081, 10367, 10657, 11857, 12799, 14449, 15487, 16927, 17297, 17671, 20401, 20807, 21217, 21631, 22897, 23327, 23761, 24199, 27847, 29767, 30257, 30751, 32257, 33799, 35377, 37537, 40897 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..42.

FORMULA

a(n) = (A129820(2*n - 1) * A129820(2*n) - 1) / 2.

EXAMPLE

For k = 26, k - 1 = 25 and k + 1 = 27 are both odd composite numbers. So (26^2 - 2) / 2 = 337 is a term of the sequence.

PROG

(PARI) k = 1; forcomposite(c = 1, 287, if(c%2 <> 0, if(c-k == 2, print1((c * (c - 2) - 1) / 2", ")); k = c))

CROSSREFS

Cf. A071904, A129820.

Sequence in context: A020358 A260540 A051962 * A214492 A157999 A152853

Adjacent sequences: A339477 A339478 A339479 * A339481 A339482 A339483

KEYWORD

nonn

AUTHOR

Dimitris Valianatos, Apr 24 2021

STATUS

approved

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Last modified December 4 19:07 EST 2022. Contains 358563 sequences. (Running on oeis4.)