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Start at (2n+1)/4 and iterate the map x -> x*ceiling(x); sequence gives number of steps for denominator to drop to 1 or 2; or -1 if this never happens.
4

%I #5 Oct 04 2012 10:28:48

%S 1,1,3,7,1,1,2,2,1,1,2,2,1,1,6,3,1,1,4,3,1,1,2,2,1,1,2,2,1,1,3,3,1,1,

%T 5,3,1,1,2,2,1,1,2,2,1,1,3,4,1,1,3,5,1,1,2,2,1,1,2,2,1,1,6,7,1,1,3,5,

%U 1,1,2,2,1,1,2,2,1,1,5,3,1,1,5,3,1,1,2,2,1,1,2,2,1,1,3,3,1,1,8,3,1,1,2,2,1

%N Start at (2n+1)/4 and iterate the map x -> x*ceiling(x); sequence gives number of steps for denominator to drop to 1 or 2; or -1 if this never happens.

%C We conjecture that the denominator always does drop.

%H J. C. Lagarias and N. J. A. Sloane, Approximate squaring (<a href="http://neilsloane.com/doc/apsq.pdf">pdf</a>, <a href="http://neilsloane.com/doc/apsq.ps">ps</a>), Experimental Math., 13 (2004), 113-128.

%Y A073341 gives number of steps until reach an integer. Cf. A085817, A085833.

%K nonn

%O 2,3

%A _N. J. A. Sloane_, Aug 16 2003