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 A189484 #18 Feb 16 2020 00:57:54
%S A189484 1,4,6,9,16,22,33,36,55,56,64,77,81,111,121,136,141,156,161,202,216,
%T A189484 256,262,276,296,303,323,351,376,393,441,454,484,505,515,516,535,545,
%U A189484 560,565,621,626,707,717,729,737,765,767,784,818,838,878,898,939,949
%N A189484 Numbers that can be factored into semiprimes which, when concatenated in increasing order, produce a palindrome.
%C A189484 This is to semiprimes A001358 as A046447 is to primes A000040.
%C A189484 The initial 1 represents the empty product.
%e A189484 The first value not itself a semiprime palindrome (A046328) or power of semiprimes (i.e., 16 = 4 * 4 which concatenate to the palindrome 44, 484 = 22^2) is 56 = 4 * 14. The first where additionally the first factor is not a single digit is 765 = 15 * 51 = 3^2 * 5 * 17 since (15, 51) are a pair of emirpimes A097393, and 765 = A158126(1).
%t A189484 ok[n_] := n == 1 || Block[{d, p = Join @@ mu /@ FactorInteger[n]}, EvenQ@ Length[p] && AnyTrue[ Union[ Sort /@ ((Times @@@ #) & /@ Union[ (Sort /@ Partition[#, 2]) & /@ Permutations[p]])], (d = Join @@ IntegerDigits[#]; d == Reverse[d]) &]]; Select[ Range[1000], ok] (* _Giovanni Resta_, Sep 15 2018 *)
%Y A189484 Cf. A001358, A002113, A046328, A046447, A097393, A158126 Products of emirpimes pairs, sorted.
%K A189484 nonn,base
%O A189484 1,2
%A A189484 _Jonathan Vos Post_, Apr 22 2011
%E A189484 Additional terms from _Franklin T. Adams-Watters_, Apr 28 2011
%E A189484 More terms from _Giovanni Resta_, Sep 15 2018