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

1,1

Comments

Intersection of A003215 and A001358.

Links

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

Example

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.

Mathematica

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

Crossrefs

Cf. A001358, A003215.

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

Sequence in context: A293647 A225908 A159961 * A119148 A166059 A226683

Adjacent sequences: A113527 A113528 A113529 * A113531 A113532 A113533

Keyword

easy,nonn

Author

Jonathan Vos Post, Jan 12 2006

Status

approved