A356424 9-gonal numbers that are semiprimes.

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

Robert Israel, Table of n, a(n) for n = 1..10000

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

Adjacent sequences: A356421 A356422 A356423 * A356425 A356426 A356427

Keyword

nonn

Author

Massimo Kofler, Aug 07 2022

Status

approved