

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
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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(ck == 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



