This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A046448 #23 Oct 25 2020 14:47:29 %S A046448 1,39,69,119,129,159,219,249,259,329,339,403,429,469,669,679,795,1207, %T A046448 1309,1329,1533,1547,1589,1703,2319,2321,2359,2649,2701,3039,3421, %U A046448 3503,3629,3633,3639,3729,3899,4303,4607,4839,5289,5295,5565,5603,5739,6209 %N A046448 Squarefree nonprimes with property that the concatenation of the prime factors is a palindrome. %e A046448 E.g., 429 = 3 * 11 * 13 -> 31113 is palindromic. %t A046448 Select[Range[6210], ! PrimeQ[#] && SquareFreeQ[#] && Reverse[x = Flatten[IntegerDigits[First /@ FactorInteger[#]]]] == x &] (* _Jayanta Basu_, Jun 24 2013 *) %t A046448 Select[Range[6500],!PrimeQ[#]&&SquareFreeQ[#]&&PalindromeQ[ FromDigits[ Flatten[ IntegerDigits/@ FactorInteger[#][[All,1]]]]]&] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Oct 25 2020 *) %Y A046448 Cf. A046447, A046449, A046450, A002113. %K A046448 nonn,base %O A046448 1,2 %A A046448 _Patrick De Geest_, Jul 15 1998 %E A046448 Definition clarified by _N. J. A. Sloane_, Oct 25 2020