OFFSET
1,1
COMMENTS
Includes all primes. - Robert Israel, Oct 25 2017
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
phi(8)=4, so 4*(8-4)+1=17.
MAPLE
filter:= proc(n) local p;
p:= numtheory:-phi(n);
isprime(p*(n-p)+1)
end proc:
select(filter, [$1..1000]); # Robert Israel, Oct 25 2017
MATHEMATICA
Select[Range[150], PrimeQ[EulerPhi[#]*(# - EulerPhi[#]) + 1] &] (* G. C. Greubel, Jan 18 2019 *)
PROG
(PARI) for (n=2, 100, if (isprime(eulerphi(n)*(n-eulerphi(n))+1), print1(n", ")))
CROSSREFS
KEYWORD
nonn
AUTHOR
Jon Perry, Jan 09 2003
EXTENSIONS
More terms from Michel Marcus, Mar 17 2014
STATUS
approved