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 A050439 #7 Oct 27 2023 22:00:44 %S A050439 39,49,55,56,60,69,74,77,78,84,93,94,95,100,105,106,110,115,119,124, %T A050439 125,126,130,133,140,141,145,152,155,156,159,162,164,165,170,174,180, %U A050439 183,184,188,189,198,201,202,203,206,207,209,212,213,218,222,225,231 %N A050439 Fifth-order composites. %H A050439 N. Fernandez, <a href="http://www.borve.org/primeness/FOP.html">An order of primeness, F(p)</a> %H A050439 N. Fernandez, <a href="/A006450/a006450.html">An order of primeness</a> [cached copy, included with permission of the author] %F A050439 Let C(n) be the n-th composite number, with C(1)=4. Then these are numbers C(C(C(C(C(n))))). %e A050439 C(C(C(C(C(8))))) = C(C(C(C(15)))) = C(C(C(25))) = C(C(38)) = C(55) = 77. So 77 is in the sequence. %p A050439 C := remove(isprime,[$4..1000]): seq(C[C[C[C[C[n]]]]],n=1..100); %Y A050439 Cf. A049076-A049081, A006450, A050435, A050436, A050438, A050440. %K A050439 easy,nonn %O A050439 1,1 %A A050439 Michael Lugo (mlugo(AT)thelabelguy.com), Dec 22 1999 %E A050439 More terms from _Asher Auel_ Dec 15 2000