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
KEYWORD
nonn
AUTHOR
K. D. Bajpai, Jul 14 2014
STATUS
approved