Bulletin of the London Mathematical Society Advance Access originally published online on March 22, 2009
Bulletin of the London Mathematical Society 2009 41(3):396-410; doi:10.1112/blms/bdp011
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© 2009 London Mathematical Society
Intermediate convergents and a metric theorem of Khinchin
Department of Mathematics
University of York
Heslington
York
YO10 5DD
United Kingdom
Received 14 August 2008.
A landmark theorem in the metric theory of continued fractions begins this way: Select a non-negative real function f defined on the positive integers and a real number x, and form the partial sums sn of f evaluated at the partial quotients a1, ..., an in the continued fraction expansion for x. Does the sequence {sn/n} have a limit as n
? In 1935 Khinchin proved that the answer is yes for almost every x, provided that the function f does not grow too quickly. In this article we are going to explore a natural reformulation of this problem in which the function f is defined on the rationals and the partial sums in question are over the intermediate convergents to x with denominators less than a prescribed amount. By using some of Khinchin's ideas together with more modern results we are able to provide a quantitative asymptotic theorem analogous to the classical one mentioned above.
2000 Mathematics Subject Classification 11B57, 11K50, 60G46.