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A240436
Semiprimes of the form n^3 - 2*n.
2
4, 21, 115, 329, 2171, 6821, 24331, 50579, 79421, 103729, 226859, 357769, 704791, 1092521, 1224829, 2048129, 2247829, 2685341, 5177371, 6967489, 9393509, 11089121, 12648871, 13651441, 16974079, 25153171, 30663671, 38272079, 46267561, 74617619, 86937421, 90517951
OFFSET
1,1
COMMENTS
Intersection of A001358 and A242135.
Since n^3 - 2*n = n * (n^2 - 2), it follows that n and (n^2 - 2) both should be prime.
LINKS
FORMULA
a(n) = A062326(n) * (A062326(n)^2 - 2). - Michel Marcus, Aug 26 2014
EXAMPLE
a(2) = 21: 3^3 - 2*3 = 27 - 6 = 21 = 3 * 7, which is semiprime.
a(3) = 115: 5^3 - 2*5 = 125 - 10 = 115 = 5 * 23, which is semiprime.
MAPLE
select(k -> numtheory:-bigomega(k)=2, [seq((n^3-2*n), n=1..500)]);
MATHEMATICA
Select[Table[n^3 - 2*n, {n, 1000}], PrimeOmega[#] == 2 &]
PROG
(PARI) forprime(p=1, 10^3, q=p^2-2; if(isprime(q), print1(p*q, ", "))) \\ Derek Orr, Aug 17 2014
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
K. D. Bajpai, Aug 17 2014
STATUS
approved