Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #10 Nov 26 2019 20:05:42
%S 1,3,5,9,11,12,17,15,16,18,31,21,41,24,25,26,59,28,67,32,33,34,83,36,
%T 38,39,40,42,109,45,127,48,49,50,51,52,157,55,56,57,179,60,191,63,64,
%U 65,211,68,69,70,72,74,241,76,77,78,80,81,277,84,283,86,87,88,90,91
%N a(1) = 1. For n > 1, a(n) = prime(n) if n is prime, else a(n) = composite(n).
%e a(9) = 16 = composite(9) as 9 is composite.
%t Join[{1},With[{comps=Select[Range[4,100],!PrimeQ[#]&]},Rest[Table[ If[ PrimeQ[n], Prime[n], comps[[n]]],{n,70}]]]] (* _Harvey P. Dale_, Nov 03 2013 *)
%Y Cf. A088608.
%K nonn
%O 1,2
%A _Amarnath Murthy_, Oct 16 2003
%E More terms from Anne Donovan (anned3005(AT)aol.com), Oct 17 2003