A080363 Nonprime numbers k such that the largest prime divisor of k is unitary.

6, 10, 12, 14, 15, 20, 21, 22, 24, 26, 28, 30, 33, 34, 35, 38, 39, 40, 42, 44, 45, 46, 48, 51, 52, 55, 56, 57, 58, 60, 62, 63, 65, 66, 68, 69, 70, 74, 76, 77, 78, 80, 82, 84, 85, 86, 87, 88, 90, 91, 92, 93, 94, 95, 96, 99, 102, 104, 105, 106, 110, 111, 112, 114, 115, 116, 117

Offset: 1

Author

Labos Elemer, Feb 21 2003

Keywords

• nonn

Examples

			k=20 is not a prime; 20 = 2*2*5, largest prime factor is 5 and gcd(5, 20/5) = 1 so 5 is a unitary prime divisor of 20, so 20 is in the sequence.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A006530, A034444, A056169.

Programs

Mathematica

ma[x_] := Part[Reverse[Flatten[FactorInteger[x]]], 2] k=0; Do[s=ma[n]; If[Equal[GCD[s, n/s], 1]&&!PrimeQ[n], Print[n]], {n, 2, 256}]