cp's OEIS Frontend

A205785 Least positive integer k such that n divides C(k)-C(j) for some j in [1,k-1], where C=A205825.

%I A205785 #6 Dec 04 2016 19:46:26
%S A205785 2,3,4,5,4,5,6,5,4,4,4,6,6,8,7,7,5,5,5,6,8,7,7,8,6,7,6,9,12,7,11,9,7,
%T A205785 10,8,6,12,7,6,8,16,8,8,9,7,12,15,9,8,6,10,7,9,6,10,9,9,12,6,8,14,11,
%U A205785 10,9,8,7,9,10,7,8,13,10,8,12,11,14,10,8,12,10,10,16,8,9,10,14
%N A205785 Least positive integer k such that n divides C(k)-C(j) for some j in [1,k-1], where C=A205825.
%C A205785 For a guide to related sequences, see A204892.
%e A205785 1 divides C(2)-C(1) -> k=2, j=1
%e A205785 2 divides C(3)-C(1) -> k=3, j=1
%e A205785 3 divides C(4)-C(3) -> k=4, j=3
%e A205785 4 divides C(5)-C(4) -> k=5, j=4
%e A205785 5 divides C(4)-C(2) -> k=4, j=2
%t A205785 s = Table[n!/Ceiling[n/2]!, {n, 1, 120}];
%t A205785 lk = Table[
%t A205785   NestWhile[# + 1 &, 1,
%t A205785    Min[Table[Mod[s[[#]] - s[[j]], z], {j, 1, # - 1}]] =!= 0 &], {z, 1,
%t A205785     Length[s]}]
%t A205785 Table[NestWhile[# + 1 &, 1,
%t A205785   Mod[s[[lk[[j]]]] - s[[#]], j] =!= 0 &], {j, 1, Length[lk]}]
%t A205785 (* _Peter J. C. Moses_, Jan 27 2012 *)
%Y A205785 Cf. A204892, A205825.
%K A205785 nonn
%O A205785 1,1
%A A205785 _Clark Kimberling_, Feb 01 2012