OFFSET
1,1
COMMENTS
If n = Product p_i^r_i then uphi(n) = Product (p_i^r_i-1); for example uphi(12) = (4-1)*(3-1) = 6.
If 2^n+1 is a Fermat prime then 2^(2*n) is a solution of the equation.
3110400 and 4294967296 are also in the sequence.
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..41 (terms < 2^35)
PROG
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
STATUS
approved