A024843 - OEIS

%I #19 Dec 14 2021 10:30:20

%S 9,23,43,69,101,139,183,233,289,361,431,518,601,703,799,916,1025,1157,

%T 1279,1426,1561,1723,1871,2048,2209,2401,2601,2783,2998,3221,3423,

%U 3661,3907,4129,4390,4659,4901,5185,5477,5739,6046,6361,6643,6973,7311,7613,7966,8327,8649

%N a(n) = least m such that if r and s in {1/1, 1/2, 1/3, ..., 1/n} satisfy r < s, then r < k/m < (k+3)/m < s for some integer k.

%C For a guide to related sequences, see A001000. - _Clark Kimberling_, Aug 08 2012

%H Clark Kimberling, <a href="/A024843/b024843.txt">Table of n, a(n) for n = 2..100</a>

%e Using the terminology introduced at A001000, the 4th separator of the set {1/3, 1/2, 1} is a(3) = 23, since 1/3 < 8/23 < 11/23 < 1/2 < 12/23 < 15/23 < 1 and 23 is the least m for which 1/3, 1/2, 1 are thus separated using numbers k/m. - _Clark Kimberling_, Aug 08 2012

%t leastSeparatorS[seq_, s_] := Module[{n = 1},

%t Table[While[Or @@ (Ceiling[n #1[[1]]] <

%t s + 1 + Floor[n #1[[2]]] &) /@ (Sort[#1, Greater] &) /@

%t Partition[Take[seq, k], 2, 1], n++]; n, {k, 2, Length[seq]}]];

%t t = Map[leastSeparatorS[1/Range[50], #] &, Range[5]];

%t TableForm[t]

%t t[[4]] (* _Peter J. C. Moses_, Aug 08 2012 *)

%Y Cf. A001000.

%K nonn

%O 2,1

%A _Clark Kimberling_