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 A073411 #20 Dec 29 2020 06:30:02 %S A073411 2,6,8,4,12,10,14,6,18,14,20,16,24,16,20,30,18,32,22,38,26,22,10,42, %T A073411 44,24,48,22,32,34,54,28,12,60,62,40,26,68,34,44,28,72,46,36,74,28,50, %U A073411 80,30,84,32,42,56,90,46,16,98,62,34,48,102,64,104,38,108,34,110,52,70 %N A073411 cototient(x) - 1 where x are the odd semiprimes (i.e., x are odd terms in A001358). %C A073411 If the Goldbach conjecture is true, all even numbers appear at least once in the sequence since pq - phi(pq) - 1 = p + q. %H A073411 Michael De Vlieger, <a href="/A073411/b073411.txt">Table of n, a(n) for n = 1..10000</a> %F A073411 a(n) = A051953(A046315(n)) - 1. - _Michel Marcus_, Jul 30 2017; corrected Dec 29 2020 %t A073411 Map[# - EulerPhi@ # - 1 &, Select[Range[1, 335, 2], PrimeOmega # == 2 &]] (* _Michael De Vlieger_, Jul 30 2017 *) %o A073411 (PARI) lista(nn) = forstep(n=1, nn, 2, if (bigomega(n)==2, print1(n-eulerphi(n)-1, ", "))); \\ _Michel Marcus_, Jul 30 2017 %Y A073411 Cf. A001358 (semiprimes), A046315 (odd semiprimes), A051953 (cototient). %K A073411 easy,nonn %O A073411 1,1 %A A073411 _Benoit Cloitre_, Aug 23 2002