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 A066072 #26 Dec 16 2024 01:56:23
%S A066072 2,3,3,5,7,5,5,7,7,13,11,13,19,13,17,17,13,19,17,13,23,17,43,19,41,37,
%T A066072 29,17,31,37,37,41,37,61,41,43,41,73,61,47,73,43,61,41,53,37,41,73,37,
%U A066072 89,73,59,97,61,61,101,37,41,109,67,73,71,113,73,73,41,73,97,61,79,83
%N A066072 Prime numbers arising in A066071.
%H A066072 Amiram Eldar, <a href="/A066072/b066072.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from Harry J. Smith)
%F A066072 a(n) = 1 + phi(A066071(n)).
%e A066072 Solutions to 1+phi(x)=13 are {13, 21, 26, 28, 36, 42}; so 13 occur 5 times in the sequence in positions 10, 13, 15, 18 and 21, obtained as 1+Phi[m] values for 5 composite arguments.
%t A066072 Select[EulerPhi@ # + 1 & /@ Complement[Range@ #, Prime@ Range@ PrimePi@ #] &@ 168, PrimeQ] (* _Michael De Vlieger_, Jul 01 2016 *)
%o A066072 (PARI) { n=0; for (m=1, 10^9, if (!isprime(m) && isprime(p=(eulerphi(m) + 1)), write("b066072.txt", n++, " ", p); if (n==1000, return)) ) } \\ _Harry J. Smith_, Nov 10 2009
%Y A066072 Cf. A000010, A058340, A066071, A066072, A066073, A066074, A066075, A066076, A066077, A066080.
%K A066072 nonn
%O A066072 1,1
%A A066072 _Labos Elemer_, Dec 03 2001