A360741 Semiprimes of the form k^2 + 4.

4, 85, 365, 445, 533, 629, 965, 1685, 1853, 2605, 2813, 3029, 3973, 4765, 5045, 5629, 5933, 6245, 6893, 8285, 8653, 11029, 11453, 11885, 12773, 14165, 15133, 16645, 17165, 17693, 20453, 21029, 22205, 22805, 23413, 24653, 27229, 29245, 29933, 30629, 32765, 34229

Offset: 1

Author

Elmo R. Oliveira, Feb 18 2023

Keywords

• nonn
• easy

Comments

A242332 gives the corresponding values of k.

Except for 4, all terms == 5 (mod 8). - Robert Israel, Feb 18 2023

Examples

			85 is a term because 9^2 + 4 = 85 = 5*17.
		

Crossrefs

Cf. A001358, A085722, A087475, A144255, A242330, A242331, A242332.

Programs

Maple

select(t -> numtheory:-bigomega(t)=2, [seq(i^2+4,i=0..1000)]); # Robert Israel, Feb 18 2023

Mathematica

Select[Range[0, 200]^2 + 4, PrimeOmega[#] == 2 &] (* Amiram Eldar, Feb 18 2023 *)

Formula

a(n) = A242332(n)^2 + 4.