OFFSET
0,2
LINKS
K. Ford, The distribution of totients, Electron. Res. Announc. Amer. Math. Soc. 4 (1998), pp. 27-34.
K. Ford, The distribution of totients, Ramanujan J. 2 (1998), pp. 67-151.
FORMULA
a(n) is about 10^n/n * 2.2655434...^((log log n)^2); see Theorem 1 in the Ford paper for a more precise asymptotic.
EXAMPLE
There are 6 totients up to 10: {1 = phi(1), 2 = phi(3), 4 = phi(5), 6 = phi(7), 8 = phi(15), 10 = phi(11)}, so a(1) = 6.
PROG
(PARI) a(n)=sum(k=1, 10^n, istotient(k))
CROSSREFS
KEYWORD
nonn,hard
AUTHOR
Charles R Greathouse IV, Feb 06 2013
EXTENSIONS
a(10) from Charles R Greathouse IV, Feb 11 2013
STATUS
approved