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 A102885 #9 Sep 10 2022 20:09:33
%S A102885 1,2,1,2,3,3,4,4,5,6,7,5,8,6,9,10,11,7,12,8,13,14,15,9,16,17,18,19,20,
%T A102885 10,21,11,22,23,24,25,26,12,27,28,29,13,30,14,31,32,33,15,34,35,36,37,
%U A102885 38,16,39,40,41,42,43,17,44,18,45,46,47,48,49,19,50,51,52,20,53,21,54
%N A102885 Index of n in the primes A000040 or nonprimes A141468.
%C A102885 The nonnegative numbers n occur exactly once in either A000040 or A141468. The sequence lists the corresponding index. It is a permutation of A008619.
%H A102885 Harvey P. Dale, <a href="/A102885/b102885.txt">Table of n, a(n) for n = 0..1000</a>
%F A102885 A141468(a(n))=n or A000040(a(n))=n.
%t A102885 Module[{nn=80,pr,np},pr=Prime[Range[PrimePi[nn]]];np=Complement[ Range[ 0,nn],pr];Table[If[PrimeQ[n],Position[pr,n],Position[np,n]],{n,0,nn}]]//Flatten (* _Harvey P. Dale_, Sep 10 2022 *)
%Y A102885 Cf. A141468, A000040, A026233.
%K A102885 nonn,easy
%O A102885 0,2
%A A102885 _Juri-Stepan Gerasimov_, Aug 17 2008
%E A102885 Edited by _R. J. Mathar_, Aug 19 2008