A124106 Octagonal numbers equal to S*(3S - 2) with 3S - 2 = k^2 and S semiprime.

96, 225, 1408, 3400, 9633, 22016, 43681, 53600, 93633, 130625, 152776, 205408, 308481, 446216, 696008, 1493896, 1628033, 3280256, 4617761, 4928008, 5595136, 6720033, 8473921, 11721633, 19995008, 20919361, 22863841, 30752008, 33340000

Offset

1,1

Links

Table of n, a(n) for n=1..29.

Eric Weisstein's World of Mathematics, Octagonal Number.

Eric Weisstein's World of Mathematics, Semiprime.

Eric Weisstein's World of Mathematics, 16-Cell

Formula

a(n) = A112392(n)*A112393(n).

Crossrefs

Cf. A112392, A112393.

Sequence in context: A110231 A108609 A125511 * A304510 A268771 A202898

Adjacent sequences: A124103 A124104 A124105 * A124107 A124108 A124109

Keyword

easy,nonn

Author

Giovanni Teofilatto, Dec 13 2006, Dec 14 2006

Status

approved