A176590 Numbers k such that both concatenation of divisors of k and reverse concatenation of divisors of k are nonprime.

1, 2, 5, 6, 8, 10, 11, 12, 14, 15, 16, 17, 18, 20, 22, 23, 24, 26, 27, 28, 29, 30, 32, 33, 34, 35, 36, 38, 40, 41, 42, 44, 45, 46, 47, 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, 82, 83, 84, 85, 86, 87, 88

Offset: 1

Author

Jaroslav Krizek, Apr 21 2010

Keywords

• nonn
• base

Comments

Numbers k such that both A037278(k) and A176558(k) are nonprime.

Examples

			10 is a term; divisors of 10: 1, 2, 5, 10; both concatenation of divisors 12510 and reverse concatenation of divisors 10521 are nonprime numbers.
Sequence of corresponding values of concatenations of divisors of a(n): 1, 12, 15, 1236, 1248, 12510, 111, ...
Sequence of corresponding values of reverse concatenations of divisors of a(n): 1, 21, 51, 6321, 8421, 10521, 111, ...
		

Crossrefs

Cf. A037278, A176558, A176554, A175354, A176589.

Formula

Intersection of A176554 and A175354. - Jason Yuen, Feb 08 2025

Extensions

Extended and revised by Charles R Greathouse IV, Apr 24 2010