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 A280327 #13 Jun 21 2019 12:08:55
%S A280327 4,12,25,39,60,94,133,183,236,320,415,520,640,805,1007,1212,1463,1800,
%T A280327 2144,2562,3021,3523,4135,4840,5747,6630,7701,9057,10392,11812,13519,
%U A280327 15400,17534,19827,22564,25624,29206,32998,37041,41819,46659,53223,59345,66104,73368,81897,91157,100827,112045
%N A280327 a(n) is obtained by applying the map k -> composite(k) n times, starting at n.
%e A280327 a(3) is 25 because the third composite is 8, the eighth composite is 15, and for the 3rd iteration, the fifteenth composite is 25.
%e A280327 To get a(4): 4 -> 9 -> 16 -> 26 -> 39.
%t A280327 c = Select[Range[10^6], CompositeQ]; Table[Nest[c[[#]] &, n, n], {n, 50}] (* _Michael De Vlieger_, Dec 31 2016 *)
%Y A280327 Cf. A002808.
%Y A280327 For primes, see A058009.
%K A280327 nonn
%O A280327 1,1
%A A280327 _Matthew Campbell_, Dec 31 2016
%E A280327 More terms from _Michael De Vlieger_, Dec 31 2016