A176554 Numbers n such that concatenations of divisors of n are nonprime.

1, 2, 4, 5, 6, 8, 10, 11, 12, 14, 15, 16, 17, 18, 19, 20, 22, 23, 24, 25, 26, 27, 28, 29, 30, 32, 33, 34, 35, 36, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 68, 69, 70, 71, 72, 74, 75, 76, 77, 78, 80, 81

Offset: 1

Author

Jaroslav Krizek, Apr 20 2010

Keywords

• nonn
• base

Comments

See A037278(n) = concatenation of divisors of n. See A176556 for corresponding values of concatenations. Complement of A176553(n) for n >= 2.

Examples

			a(6) = 8: divisors of 8 are 1,2,4,8 and their concatenation 1248 is nonprime.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Programs

Mathematica

Select[Range[100],!PrimeQ[FromDigits[Flatten[IntegerDigits/@ Divisors[ #]]]]&] (* Harvey P. Dale, Jul 09 2021 *)

Extensions

Edited and extended by Charles R Greathouse IV, Apr 30 2010