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 A050440 #7 Oct 27 2023 22:00:44 %S A050440 56,69,77,78,84,94,100,105,106,115,124,125,126,133,140,141,145,152, %T A050440 156,162,164,165,170,174,183,184,188,198,202,203,206,209,212,213,218, %U A050440 222,231,235,236,242,243,253,256,258,259,262,264,266,270,272,278,284 %N A050440 Sixth-order composites. %H A050440 N. Fernandez, <a href="http://www.borve.org/primeness/FOP.html">An order of primeness, F(p)</a> %H A050440 N. Fernandez, <a href="/A006450/a006450.html">An order of primeness</a> [cached copy, included with permission of the author] %F A050440 Let C(n) be the n-th composite number, with C(1)=4. Then these are numbers C(C(C(C(C(C(n)))))). %e A050440 C(C(C(C(C(C(1)))))) = C(C(C(C(C(4))))) = C(C(C(C(9)))) = C(C(C(16))) = C(C(26)) = C(39) = 56. So 56 is in the sequence. So 77 is in the sequence. %p A050440 C := remove(isprime,[$4..1000]): seq(C[C[C[C[C[C[n]]]]]],n=1..100); %Y A050440 Cf. A049076-A049081, A006450, A050435, A050436, A050438, A050439. %K A050440 easy,nonn %O A050440 1,1 %A A050440 Michael Lugo (mlugo(AT)thelabelguy.com), Dec 22 1999 %E A050440 More terms from _Asher Auel_ Dec 15 2000