OFFSET
1,4
COMMENTS
Let c(1)=1 and c(k+1)=n*phi(c(k)). Then c(k+1)/c(k) is a decreasing sequence of integers, so eventually becomes constant. a(n) is the ratio between terms once that becomes constant. (In fact, as soon as a ratio repeats, it remains constant from that point on.)
FORMULA
If p prime, a(p)=a(p-1). If every prime divisor of m divides n, a(n*m)=a(n)*m.
EXAMPLE
For n=25, the sequence m -> n*phi(m) is 1,25,500,5000,50000,...; the ratios are 25,20,10,10,...; so a(25)=10.
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Franklin T. Adams-Watters, Sep 19 2005
EXTENSIONS
Definition revised by N. J. A. Sloane, Mar 12 2016
STATUS
approved