OFFSET
1,2
COMMENTS
A039698 with the primes removed. For every prime p, 2p is in the sequence. - Ray Chandler, May 26 2008
LINKS
Iain Fox, Table of n, a(n) for n = 1..10000 (first 1000 terms from Harry J. Smith)
EXAMPLE
Solutions to 1+phi(x)=13 are {13, 21, 26, 28, 36, 42} of which the 5 composites are in the sequence.
MAPLE
select(n -> not isprime(n) and isprime(1+numtheory:-phi(n)), [$1..1000]); # Robert Israel, Dec 29 2017
MATHEMATICA
Select[Complement[Range@ #, Prime@ Range@ PrimePi@ #] &@ 150, PrimeQ[EulerPhi@ # + 1] &] (* Michael De Vlieger, Jul 01 2016 *)
PROG
(PARI) { n=0; for (m=1, 10^9, if (!isprime(m) && isprime(eulerphi(m) + 1), write("b066071.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Nov 10 2009
(Magma) [n: n in [1..200] |not IsPrime(n) and IsPrime(EulerPhi(n)+1)]; // Vincenzo Librandi, Jul 02 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Dec 03 2001
STATUS
approved