OFFSET
1,1
COMMENTS
Makowski shows that a k exists for each n. It appears that k<=2n. For prime n, it appears that n-1<=k<=2n.
REFERENCES
R. K. Guy, Unsolved Problems in Number Theory, 3rd Ed., New York, Springer-Verlag, 2004, Section B36.
Andrzej Makowski, On the equation phi(n+k)=2*phi(n), Elem. Math., 29 (1974), 13.
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..10000
MATHEMATICA
Table[k=1; e=EulerPhi[n]; While[EulerPhi[n+k] != 2e, k++ ]; k, {n, 100}]
CROSSREFS
KEYWORD
nonn
AUTHOR
T. D. Noe, Jul 15 2005
STATUS
approved