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

1,2

Comments

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

Links

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

Example

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

Mathematica

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

Crossrefs

Sequence in context: A035500 A080653 A115836 * A366322 A284895 A285354

Adjacent sequences: A176551 A176552 A176553 * A176555 A176556 A176557

Keyword

nonn,base

Author

Jaroslav Krizek, Apr 20 2010

Extensions

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

Status

approved