A113527 Semiprimes in A056108.

15, 115, 155, 201, 253, 445, 785, 1345, 2215, 3503, 3711, 4145, 4841, 5853, 6395, 7855, 9131, 12353, 13535, 14353, 16503, 18331, 19281, 20255, 20751, 21253, 21761, 23853, 24935, 26603, 29503, 30101

Offset: 1

Author

Jonathan Vos Post, Jan 12 2006

Keywords

• easy
• nonn

Comments

Intersection of A056108 and A001358.

Examples

			a(1) = 15 because A056108(2) = 15 = 3 * 5 is semiprime.
a(2) = 115 because A056108(6) = 115 = 5 * 23 is semiprime.
a(32) = 30101 because A056108(100) = 30101 = 31 * 971 is semiprime.
		

Links

• Michael De Vlieger, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A001358, A056108.

Cf. A113519, A113524, A113525, A113528, A113530.

Programs

Mathematica

Select[Array[3 #^2 + # + 1 &, 100], PrimeOmega[#] == 2 &] (* Michael De Vlieger, Mar 17 2021 *)

Formula

{a(n)} = {3*n^2 + n + 1 iff semiprime}. {a(n)} = A056108 INTERSECT A001358.