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 A066071 #38 Dec 14 2024 20:31:02
%S A066071 1,4,6,8,9,10,12,14,18,21,22,26,27,28,32,34,36,38,40,42,46,48,49,54,
%T A066071 55,57,58,60,62,63,74,75,76,77,82,86,88,91,93,94,95,98,99,100,106,108,
%U A066071 110,111,114,115,117,118,119,122,124,125,126,132,133,134,135,142,145,146
%N A066071 Nonprime numbers k such that phi(k) + 1 is prime.
%C A066071 A039698 with the primes removed. For every prime p, 2p is in the sequence. - _Ray Chandler_, May 26 2008
%C A066071 Includes 3*p for p in A005382 and p^2 for p in A065508. - _Robert Israel_, Dec 29 2017
%H A066071 Iain Fox, <a href="/A066071/b066071.txt">Table of n, a(n) for n = 1..10000</a> (first 1000 terms from Harry J. Smith)
%e A066071 Solutions to 1+phi(x)=13 are {13, 21, 26, 28, 36, 42} of which the 5 composites are in the sequence.
%p A066071 select(n -> not isprime(n) and isprime(1+numtheory:-phi(n)), [$1..1000]); # _Robert Israel_, Dec 29 2017
%t A066071 Select[Complement[Range@ #, Prime@ Range@ PrimePi@ #] &@ 150, PrimeQ[EulerPhi@ # + 1] &] (* _Michael De Vlieger_, Jul 01 2016 *)
%o A066071 (PARI) isok(k) = { !isprime(k) && isprime(eulerphi(k) + 1) } \\ _Harry J. Smith_, Nov 10 2009
%o A066071 (Magma) [n: n in [1..200] |not IsPrime(n) and IsPrime(EulerPhi(n)+1)]; // _Vincenzo Librandi_, Jul 02 2016
%Y A066071 Cf. A000010, A000040, A005382, A006093, A039649, A039698, A058339, A058340, A065508, A066072, A066073, A066074, A066075, A066076, A066077, A066080.
%K A066071 nonn
%O A066071 1,2
%A A066071 _Labos Elemer_, Dec 03 2001