A046448 Squarefree nonprimes with property that the concatenation of the prime factors is a palindrome.

1, 39, 69, 119, 129, 159, 219, 249, 259, 329, 339, 403, 429, 469, 669, 679, 795, 1207, 1309, 1329, 1533, 1547, 1589, 1703, 2319, 2321, 2359, 2649, 2701, 3039, 3421, 3503, 3629, 3633, 3639, 3729, 3899, 4303, 4607, 4839, 5289, 5295, 5565, 5603, 5739, 6209

Offset: 1

Author

Patrick De Geest, Jul 15 1998

Keywords

• nonn
• base

Examples

			E.g., 429 = 3 * 11 * 13 -> 31113 is palindromic.
		

Crossrefs

Cf. A046447, A046449, A046450, A002113.

Programs

Mathematica

Select[Range[6210], ! PrimeQ[#] && SquareFreeQ[#] && Reverse[x = Flatten[IntegerDigits[First /@ FactorInteger[#]]]] == x &] (* Jayanta Basu, Jun 24 2013 *)
Select[Range[6500],!PrimeQ[#]&&SquareFreeQ[#]&&PalindromeQ[ FromDigits[ Flatten[ IntegerDigits/@ FactorInteger[#][[All,1]]]]]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Oct 25 2020 *)

Extensions

Definition clarified by N. J. A. Sloane, Oct 25 2020