A039778 phi(n) is equal to the sum of prime factors and exponents of n+1.

32, 38, 54, 56, 84, 20720

Offset: 1

Author

Olivier Gérard

Keywords

• nonn
• more
• hard

Comments

a(7) > 10^8. - Naohiro Nomoto, Jun 21 2001

a(7) > 10^9. - Michel Marcus, Jun 03 2014

a(7) > 10^12. - Giovanni Resta, Jun 11 2016

Examples

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

Crossrefs

Cf. A000010, A008474.

Programs

Mathematica

Select[Range[30000], EulerPhi[#] == Plus @@ Flatten@ FactorInteger[# + 1] &] (* Giovanni Resta, Jun 11 2016 *)

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