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A205840 [s(k)-s(j)]/2, where the pairs (k,j) are given by A205837 and A205838. 45

%I #15 Jul 28 2020 11:13:59

%S 1,2,1,3,6,5,4,10,9,8,4,16,13,27,26,25,21,17,44,43,42,38,34,17,71,68,

%T 55,116,115,114,110,106,89,72,188,187,186,182,178,161,144,72,304,301,

%U 288,233,493,492,491,487,483,466,449,377,305,798,797,796,792,788

%N [s(k)-s(j)]/2, where the pairs (k,j) are given by A205837 and A205838.

%C Let s(n)=F(n+1), where F=A000045 (Fibonacci numbers), so that s=(1,2,3,5,8,13,21,...). If c is a positive integer, there are infinitely many pairs (k,j) such that c divides s(k)-s(j). The set of differences s(k)-s(j) is ordered as a sequence at A204922. Guide to related sequences:

%C c....k..........j..........s(k)-s(j)....[s(k)-s(j)]/c

%C 2....A205837....A205838....A205839......A205840

%C 3....A205842....A205843....A205844......A205845

%C 4....A205847....A205848....A205849......A205850

%C 5....A205852....A205853....A205854......A205855

%C 6....A205857....A205858....A205859......A205860

%C 7....A205862....A205863....A205864......A205865

%C 8....A205867....A205868....A205869......A205870

%C 9....A205872....A205873....A205874......A205875

%C 10...A205877....A205878....A205879......A205880

%e The first six terms match these differences:

%e s(3)-s(1) = 3-1 = 2 = 2*1

%e s(4)-s(1) = 5-1 = 4 = 2*2

%e s(4)-s(3) = 5-3 = 2 = 2*1

%e s(5)-s(2) = 8-2 = 6 = 2*3

%e s(6)-s(1) = 13-1 = 12 = 2*6

%e s(6)-s(3) = 13-3 = 10 = 2*5

%t s[n_] := s[n] = Fibonacci[n + 1]; z1 = 400; z2 = 60;

%t f[n_] := f[n] = Floor[(-1 + Sqrt[8 n - 7])/2];

%t Table[s[n], {n, 1, 30}]

%t u[m_] := u[m] = Flatten[Table[s[k] - s[j], {k, 2, z1}, {j, 1, k - 1}]][[m]]

%t Table[u[m], {m, 1, z1}] (* A204922 *)

%t v[n_, h_] := v[n, h] = If[IntegerQ[u[h]/n], h, 0]

%t w[n_] := w[n] = Table[v[n, h], {h, 1, z1}]

%t d[n_] := d[n] = Delete[w[n], Position[w[n], 0]]

%t c = 2; t = d[c] (* A205556 *)

%t k[n_] := k[n] = Floor[(3 + Sqrt[8 t[[n]] - 1])/2]

%t j[n_] := j[n] = t[[n]] - f[t][[n]] (f[t[[n]]] + 1)/2

%t Table[k[n], {n, 1, z2}] (* A205837 *)

%t Table[j[n], {n, 1, z2}] (* A205838 *)

%t Table[s[k[n]] - s[j[n]], {n, 1, z2}](* A205839 *)

%t Table[(s[k[n]] - s[j[n]])/c, {n, 1, z2}] * A205840 *)

%Y Cf. A204890, A205587, A205839.

%K nonn

%O 1,2

%A _Clark Kimberling_, Feb 01 2012

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Last modified March 28 20:05 EDT 2024. Contains 371254 sequences. (Running on oeis4.)