OFFSET
1,2
LINKS
Vaclav Kotesovec, Table of n, a(n) for n = 1..3280
Vaclav Kotesovec, Plot of a(n)/(n*2^n) for n = 1..5000
Eric Weisstein's World of Mathematics, Totient Function.
Wikipedia, Euler's totient function.
FORMULA
a(n) ~ 3 * n * 2^n / Pi^2.
MATHEMATICA
Table[Sum[Binomial[n, k]*EulerPhi[k], {k, 1, n}], {n, 1, 40}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Vaclav Kotesovec, Mar 18 2019
STATUS
approved