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 A050436 #13 Oct 27 2023 22:00:44 %S A050436 16,21,25,26,28,33,36,38,39,42,48,49,50,52,55,56,57,60,64,68,69,70,72, %T A050436 74,77,78,80,84,87,88,90,93,94,95,98,100,104,105,106,110,111,115,117, %U A050436 118,119,121,122,124,125,126,130,133,135,138,140,141,145,146,147 %N A050436 Third-order composites. %H A050436 N. Fernandez, <a href="http://www.borve.org/primeness/FOP.html">An order of primeness, F(p)</a> %H A050436 N. Fernandez, <a href="/A006450/a006450.html">An order of primeness</a> [cached copy, included with permission of the author] %F A050436 Let C(n) be the n-th composite number, with C(1)=4. Then these are numbers C(C(C(n))). %e A050436 C(C(C(8))) = C(C(15)) = C(25) = 38. So 38 is in the sequence. %p A050436 C := remove(isprime,[$4..1000]): seq(C[C[C[C[n]]]],n=1..100); %t A050436 Nest[Values@ KeySelect[MapIndexed[First@ #2 -> #1 &, #], CompositeQ] &, Select[Range@ 150, CompositeQ], 2] (* _Michael De Vlieger_, Jul 22 2017 *) %Y A050436 Cf. A049076, A049077, A049078, A049079, A049080, A049081, A006450, A050435, A050438, ... %K A050436 easy,nonn %O A050436 1,1 %A A050436 Michael Lugo (mlugo(AT)thelabelguy.com), Dec 22 1999 %E A050436 More terms from _Asher Auel_ Dec 15 2000