OFFSET
1,2
COMMENTS
a(n)+1 is prime except for a(5)=8.
Superset of A070689. Is a(5)=8 the only additional value? - Ralf Stephan, Feb 11 2004
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MATHEMATICA
Select[Range[2000], EulerPhi[#^2 + 1] == #*EulerPhi[# + 1] &] (* Amiram Eldar, Nov 21 2020 *)
PROG
(PARI) isok(k) = eulerphi(k^2+1) == k*eulerphi(k+1); \\ Michel Marcus, Nov 21 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Feb 05 2002
STATUS
approved