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 A171521 #12 Jan 21 2023 11:32:18
%S A171521 1,2,3,5,6,7,8,9,10,11,13,14,15,16,17,18,19,20,21,22,23,25,26,27,28,
%T A171521 29,30,31,32,33,34,35,37,38,39,40,41,42,43,44,45,46,47,48,49,51,52,53,
%U A171521 54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,73,74,75
%N A171521 Numbers that are not the product of k-th composite number and k for any k >= 1.
%C A171521 Complement of A071228.
%t A171521 Module[{nn=150,cmps},cmps=Select[Range[nn],CompositeQ];Complement[ Range[ Length[cmps]],Times@@@Thread[{cmps,Range[Length[cmps]]}]]] (* _Harvey P. Dale_, Jan 21 2023 *)
%Y A171521 Cf. A002808, A071228.
%K A171521 nonn
%O A171521 1,2
%A A171521 _Jaroslav Krizek_, Dec 11 2009
%E A171521 More terms from _Hugo Pfoertner_, Jan 17 2022