A039778 - OEIS

%I #14 Jun 11 2016 07:57:26

%S 32,38,54,56,84,20720

%N phi(n) is equal to the sum of prime factors and exponents of n+1.

%C a(7) > 10^8. - _Naohiro Nomoto_, Jun 21 20a

%C a(7) > 10^9. - _Michel Marcus_, Jun 03 2014

%C a(7) > 10^12. - _Giovanni Resta_, Jun 11 2016

%e phi(38)=18, 39=3^1*13^1, 3+1+13+1=18.

%t Select[Range[30000], EulerPhi[#] == Plus @@ Flatten@ FactorInteger[# + 1] &] (* _Giovanni Resta_, Jun 11 2016 *)

%o (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

%Y Cf. A000010, A008474.

%K nonn,more

%O 1,1

%A _Olivier Gérard_