cp's OEIS Frontend

A227688 Numerator of least splitting rational of s(n) and s(n+1), where s(n) = 1/sqrt(1) + 1/sqrt(2) + ... + 1/sqrt(n).

%I A227688 #7 Jun 24 2015 18:38:59
%S A227688 1,2,5,3,7,4,13,9,5,21,11,17,6,19,13,20,7,22,15,23,8,41,25,17,26,9,46,
%T A227688 28,19,29,49,10,41,31,21,32,54,11,45,34,23,35,47,12,73,49,37,25,38,64,
%U A227688 13,79,53,40,27,41,55,97,14,71,43,72,29,44,59,104,15
%N A227688 Numerator of least splitting rational of s(n) and s(n+1), where s(n) = 1/sqrt(1) + 1/sqrt(2) + ... + 1/sqrt(n).
%C A227688 Suppose that x < y.  The least splitter of x and y is introduced at A227631 as the least positive integer d such that x <= c/d < y for some integer c; the number c/d is called the least splitting rational of x and y.
%H A227688 Clark Kimberling, <a href="/A227688/b227688.txt">Table of n, a(n) for n = 1..1000</a>
%e A227688 The denominators (A227687) and numerators (A227688) can be read from these chains:
%e A227688 1 < 2 < 5/2 < 3 < 7/2 < 4 < 13/3 < 9/2 < 5 < 21/4 < 11/2 < 17/3 < 6 < . . . ;
%e A227688 s(1) <= 1 < s(2) < 2 < s(3) < 5/2 < s(4) < 3 < s(5) < 4 < s(6) < 13/3 <  . . .
%t A227688 r[x_, y_] := Module[{c, d}, d = NestWhile[#1 + 1 &, 1, ! (c = Ceiling[#1 x - 1]) < Ceiling[#1 y] - 1 &]; (c + 1)/d];
%t A227688 s[n_] := s[n] = Sum[k^(-1/2), {k, 1, n}]; t = Table[r[s[n], s[n + 1]], {n, 1, 15}] (*fractions*)
%t A227688 fd = Denominator[t] (*A227687*)
%t A227688 fn = Numerator[t]   (*A227688*)
%Y A227688 Cf. A227631, A227687.
%K A227688 nonn,frac,easy
%O A227688 1,2
%A A227688 _Clark Kimberling_, Jul 21 2013