A039789 Integers k such that phi(k) is equal to the product of (the sum of prime factors and the sum of exponents) of k+1.

7, 15, 62, 65, 76, 98, 260, 980

Offset

1,1

Comments

Next term if it exists is greater than 1500000. - Reiner Martin, May 20 2001

No further terms up to 20000000. - Harvey P. Dale, Apr 19 2013

Links

Table of n, a(n) for n=1..8.

Example

phi(62)=30, 63=3^2*7^1, (3+7)*(2+1)=30.

Mathematica

epQ[n_]:=Module[{fi=Transpose[FactorInteger[n+1]]}, EulerPhi[n]== Total[ First[fi]]* Total[Last[fi]]]; Select[Range[1000], epQ] (* Harvey P. Dale, Apr 19 2013 *)

Prog

(PARI) isok(k) = my(f=factor(k+1)); eulerphi(k) == vecsum(f[, 1]) * vecsum(f[, 2]); \\ Michel Marcus, Oct 30 2022

Crossrefs

Cf. A000010, A039697.

Sequence in context: A141548 A146159 A187986 * A279882 A171064 A042313

Adjacent sequences: A039786 A039787 A039788 * A039790 A039791 A039792

Keyword

nonn,more

Author

Olivier Gérard

Status

approved