OFFSET
1,1
COMMENTS
a(7) > 10^8. - Naohiro Nomoto, Jun 21 20a
a(7) > 10^9. - Michel Marcus, Jun 03 2014
a(7) > 10^12. - Giovanni Resta, Jun 11 2016
EXAMPLE
phi(38)=18, 39=3^1*13^1, 3+1+13+1=18.
MATHEMATICA
Select[Range[30000], EulerPhi[#] == Plus @@ Flatten@ FactorInteger[# + 1] &] (* Giovanni Resta, Jun 11 2016 *)
PROG
(PARI) isok(n) = (f = factor(n+1)) && (sum(i=1, #f~, f[i, 2]) + sum(i=1, #f~, f[i, 1]) == eulerphi(n)); \\ Michel Marcus, Jun 03 2014
CROSSREFS
KEYWORD
nonn,more
AUTHOR
STATUS
approved