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A356424
9-gonal numbers that are semiprimes.
1
9, 46, 111, 559, 1639, 3961, 4699, 7291, 11629, 12871, 23329, 30691, 32689, 41311, 48439, 85879, 114211, 129889, 142309, 159751, 262081, 267859, 310069, 342109, 389611, 418141, 486019, 542341, 584461, 619291, 729829, 758881, 923401, 967051, 1011709, 1104049, 1163809
OFFSET
1,1
LINKS
EXAMPLE
9 = 3 * 3 = 2*(7* 2 - 5)/2.
3961 = 17 * 233 = 34*(7* 34 - 5)/2.
41311 = 109 * 379 = 109*(7*109 - 5)/2.
758881 = 233 * 3257 = 466*(7*466 - 5)/2.
MAPLE
R:= NULL: count:= 0:
for i from 1 while count < 100 do
v:= i*(7*i-5)/2;
if numtheory:-bigomega(v) = 2 then R:= R, v; count:= count+1 fi
od:
R; # Robert Israel, Jan 15 2023
MATHEMATICA
Select[Table[n*(7*n - 5)/2, {n, 1, 600}], PrimeOmega[#] == 2 &] (* Amiram Eldar, Aug 07 2022 *)
CROSSREFS
Intersection of A001106 and A001358.
Sequence in context: A224851 A042003 A117052 * A280852 A009294 A061620
KEYWORD
nonn
AUTHOR
Massimo Kofler, Aug 07 2022
STATUS
approved