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 A171576 #15 Mar 01 2020 15:35:42
%S A171576 1,2,3,3,3,1,1,1,1,3,7,7,11,13,13,15,19,23,23,27,29,29,33,35,39,45,47,
%T A171576 47,49,49,51,63,65,69,69,77,77,81,85,87,91,95,95,103,103,105,105,115,
%U A171576 125,127,127,129,133,133,141,145,149,153,153,157,159,159,167,179,181
%N A171576 a(n) = abs(n-th noncomposite number minus n-th even nonprime number).
%H A171576 Harvey P. Dale, <a href="/A171576/b171576.txt">Table of n, a(n) for n = 1..1000</a>
%F A171576 a(n) = abs(A008578(n) - A163300(n)).
%e A171576 a(1) = abs(1-0) = 1, a(2) = abs(2-4) = 2, a(3) = abs(3-6) = 3.
%t A171576 Module[{nn=400,nc,enp,len},nc=Select[Range[nn],!CompositeQ[#]&];enp= Join[{0},Range[4,nn,2]];len=Min[Length[nc],Length[enp]];Abs[#[[1]]- #[[2]]]&/@Thread[{Take[nc,len],Take[enp,len]}]] (* _Harvey P. Dale_, Mar 01 2020 *)
%Y A171576 Cf. A008578 (noncomposite), A163300 (even nonprime).
%K A171576 nonn
%O A171576 1,2
%A A171576 _Juri-Stepan Gerasimov_, Dec 12 2009
%E A171576 Corrected (a 67 replaced by another 69) by _R. J. Mathar_, May 22 2010