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 A320894 #8 Feb 07 2021 06:25:54
%S A320894 4,9,16,24,25,36,40,49,54,56,64,81,88,96,100,104,121,135,136,144,152,
%T A320894 160,169,184,189,196,216,224,225,232,240,248,250,256,289,296,297,324,
%U A320894 328,336,344,351,352,360,361,375,376,384,400,416,424,441,459,472,484
%N A320894 Numbers with an even number of prime factors (counted with multiplicity) that cannot be factored into distinct squarefree semiprimes.
%C A320894 A squarefree semiprime (A006881) is a product of any two distinct primes.
%H A320894 Amiram Eldar, <a href="/A320894/b320894.txt">Table of n, a(n) for n = 1..10000</a>
%e A320894 A complete list of all strict factorizations of 24 is: (2*3*4), (2*12), (3*8), (4*6), (24). All of these contain at least one number that is not a squarefree semiprime, so 24 belongs to the sequence.
%t A320894 strsqfsemfacs[n_]:=If[n<=1,{{}},Join@@Table[Map[Prepend[#,d]&,Select[strsqfsemfacs[n/d],Min@@#>d&]],{d,Select[Rest[Divisors[n]],And[SquareFreeQ[#],PrimeOmega[#]==2]&]}]];
%t A320894 Select[Range[100],And[EvenQ[PrimeOmega[#]],strsqfsemfacs[#]=={}]&]
%Y A320894 Cf. A001055, A001358, A005117, A006881, A007717, A028260, A318871, A318953, A320655, A320656, A320891, A320892, A320893.
%K A320894 nonn
%O A320894 1,1
%A A320894 _Gus Wiseman_, Oct 23 2018