A039782 phi(n) is equal to the sum of the prime-power components of n-1.

3, 5, 16, 17, 22, 36, 40, 257, 65537

Offset

1,1

Comments

Close to Fermat primes (A019434). Next term if it exists is greater than 10^8. - Jud McCranie, Dec 09 1999

Next term > 10^9. - Michel Marcus, Jun 03 2014

a(10) > 10^13, if it exists. - Giovanni Resta, Dec 03 2018

Links

Table of n, a(n) for n=1..9.

Example

phi(36)=12, 35=5^1*7^1, (5^1)+(7^1)=12.

Mathematica

Select[Range[3, 66000], EulerPhi[#]==Total[#[[1]]^#[[2]]&/@FactorInteger[ #-1]]&] (* Harvey P. Dale, Nov 30 2018 *)

Prog

(PARI) isok(n) = (f = factor(n-1)) && (sum(i=1, #f~, f[i, 1]^f[i, 2]) == eulerphi(n)); \\ Michel Marcus, Jun 03 2014

Crossrefs

Cf. A000010, A008475.

Sequence in context: A325257 A006593 A115724 * A331638 A080056 A330055

Adjacent sequences: A039779 A039780 A039781 * A039783 A039784 A039785

Keyword

nonn,more

Author

Olivier Gérard, Dec 11 1999

Status

approved