A176589 Numbers k such that both concatenation of divisors of k and reverse concatenation of divisors of k are noncomposite.

1, 3, 7, 13, 31, 97, 103, 109, 151, 181, 193, 367, 409, 439, 487, 523, 571, 601, 613, 733, 811, 823, 1069, 1117, 1279, 1483, 1489, 1579, 1597, 1789, 1831, 1867, 1897, 1939, 2161, 2203, 2239, 2251, 2269, 2281, 2437, 2503, 2509, 2539, 2659, 2671, 2689, 2953

Offset: 1

Author

Jaroslav Krizek, Apr 21 2010

Keywords

• nonn
• base

Comments

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

Examples

			31 is a term; divisors of 31: 1, 31; both concatenation of divisors 131 and reverse concatenation of divisors 311 are noncomposite.
1897 is a term; divisors of 1897: 1, 7, 271, 1897; both concatenation of divisors 172711897 and reverse concatenation of divisors 189727171 are noncomposite.
Sequence of corresponding values of concatenations of divisors of a(n): 1, 13, 17, 113, 131, 197, ...
Sequence of corresponding values of reverse concatenations of divisors of a(n): 1, 31, 71, 131, 311, 971, ...
		

Crossrefs

Cf. A037278, A176558, A176553, A089374, A176590.

Formula

Intersection of A176553 and A089374. - Jason Yuen, Feb 08 2025

Extensions

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