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A245232
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Semiprimes of the form (2*n^3+n)/3.
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1
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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
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OFFSET
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1,1
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COMMENTS
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The n-th octahedral number = (2*n^3+n)/3.
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LINKS
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EXAMPLE
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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.
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MAPLE
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select(t -> numtheory:-bigomega(t)=2, [seq((2*n^3+n)/3, n=1..1000)]); # Robert Israel, Jul 15 2014
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MATHEMATICA
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Select[Table[(2*n^3 + n)/3, {n, 500}], PrimeOmega[#] == 2 &]
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PROG
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(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
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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