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A245232 Semiprimes of the form (2*n^3+n)/3. 1
6, 85, 146, 489, 1469, 3281, 4579, 6181, 8119, 19871, 23969, 99269, 238631, 439031, 470009, 536269, 961969, 1240619, 1365631, 2579981, 2887219, 3105031, 3696881, 3953221, 5096981, 5413801, 7002379, 8006069, 8874781, 22050881, 23310631, 27854731, 34596869, 40465769 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Semiprimes in A005900.

The n-th octahedral number = (2*n^3+n)/3.

LINKS

K. D. Bajpai, Table of n, a(n) for n = 1..8050

EXAMPLE

n=5: (2*n^3 + n)/3 = 85 = 5 * 17 which is semiprime. Hence 85 appears in the sequence.

n=9: (2*n^3 + n)/3 = 489 = 3 * 163 which is semiprime. Hence 489 appears in the sequence.

MAPLE

select(t -> numtheory:-bigomega(t)=2, [seq((2*n^3+n)/3, n=1..1000)]); # Robert Israel, Jul 15 2014

MATHEMATICA

Select[Table[(2*n^3 + n)/3, {n, 500}], PrimeOmega[#] == 2 &]

PROG

(PARI) s=[]; for(n=1, 500, m=(2*n^3+n); if(m%3==0 && bigomega(m\3)==2, s=concat(s, m\3))); s \\ Colin Barker, Jul 15 2014

CROSSREFS

Cf. A001358, A005900.

Sequence in context: A244961 A293455 A295229 * A284522 A167252 A290011

Adjacent sequences:  A245229 A245230 A245231 * A245233 A245234 A245235

KEYWORD

nonn

AUTHOR

K. D. Bajpai, Jul 14 2014

STATUS

approved

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Last modified November 16 17:39 EST 2018. Contains 317275 sequences. (Running on oeis4.)