A113530 Semiprimes in A003215.

91, 169, 217, 469, 721, 817, 1027, 1141, 1261, 1387, 2611, 2977, 3781, 3997, 4681, 5677, 5941, 6487, 6769, 7651, 7957, 8587, 9577, 10981, 11347, 12481, 12871, 14077, 14491, 15769, 16207, 17557, 18019, 18961, 20419, 20917, 21421, 22969, 24031

Offset: 1

Author

Jonathan Vos Post, Jan 12 2006

Keywords

• easy
• nonn

Comments

Intersection of A003215 and A001358.

Examples

			a(1) = 91 because A003215(5) = (5+1)^3 - 5^3 = 91 = 7 * 13 is semiprime.
a(7) = 121 because A003215(7) = (7+1)^3 - 7^3 = 169 = 13^2 is semiprime; the two prime factors need not be distinct.
		

Links

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

Crossrefs

Cf. A001358, A003215.

Cf. A113519, A113524, A113525, A113527, A113528.

Programs

Mathematica

Select[Array[3 #^2 + 3 # + 1 &, 90], PrimeOmega[#] == 2 &] (* Michael De Vlieger, Mar 17 2021 *)