A380069 Semiprime 12-gonal numbers.

33, 217, 793, 4681, 6697, 9073, 22177, 58969, 80137, 96049, 113401, 132193, 197209, 221761, 289441, 382537, 470017, 607609, 671977, 694153, 935713, 1042417, 1069993, 1493857, 1627921, 1803601, 1876393, 2181961, 2261953, 2510569, 2639737, 2727649, 3093697, 3285361, 3383353

Offset: 1

Author

Massimo Kofler, Jan 11 2025

Keywords

• nonn

Comments

All terms are odd.

Examples

			33 = 3*11 is the product of 2 prime number and is a dodecagonal number = 3*(5*3-4).
217 = 7*31 is the product of 2 prime number and is a dodecagonal number = 7*(5*7-4).
793 = 13*61 is the product of 2 prime number and is a dodecagonal number = 13*(5*13-4).
		

Crossrefs

Intersection of A001358 and A051624.

Cf. A000384.

Programs

Mathematica

Table[k*(5*k-4), {k, Select[Range[850], And @@ PrimeQ[{#, 5*#-4}] &]}] (* Amiram Eldar, Jan 11 2025 *)

PARI

select(x->bigomega(x)==2, vector(1000, n, n*(5*n-4))) \\ Michel Marcus, Jan 20 2025