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

32, 38, 54, 56, 84, 20720

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

Links

Table of n, a(n) for n=1..6.

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

Cf. A000010, A008474.

Sequence in context: A070624 A345491 A178099 * A354422 A217060 A326112

Adjacent sequences: A039775 A039776 A039777 * A039779 A039780 A039781

Keyword

nonn,more

Author

Olivier Gérard

Status

approved