A205010 Least k such that n divides s(k)-s(j) for some j satisfying 1<=j

2, 3, 4, 3, 3, 4, 4, 5, 4, 5, 8, 7, 6, 4, 8, 5, 5, 4, 4, 8, 7, 8, 5, 7, 5, 6, 7, 7, 6, 8, 12, 5, 8, 5, 8, 10, 10, 8, 9, 9, 6, 7, 16, 8, 10, 11, 8, 7, 8, 5, 7, 10, 8, 7, 10, 7, 8, 6, 20, 8

Offset: 1

Author

Clark Kimberling, Jan 22 2012

Keywords

• nonn

Comments

See A204892 for a discussion and guide to related sequences.

Crossrefs

Cf. A000984, A204892, A205008.

Programs

Mathematica

s[n_] := s[n] = Binomial[2 (n - 1), n - 1];
 z1 = 700; z2 = 60;
Table[s[n], {n, 1, 30}]   (* A000984 *)
u[m_] := u[m] = Flatten[Table[s[k] - s[j], {k, 2, z1}, {j, 1, k - 1}]][[m]]
Table[u[m], {m, 1, z1}]   (* A205008 *)
v[n_, h_] := v[n, h] = If[IntegerQ[u[h]/n], h, 0]
w[n_] := w[n] = Table[v[n, h], {h, 1, z1}]
d[n_] := d[n] = First[Delete[w[n], Position[w[n], 0]]]
Table[d[n], {n, 1, z2}]   (* A205009 *)
k[n_] := k[n] = Floor[(3 + Sqrt[8 d[n] - 1])/2]
m[n_] := m[n] = Floor[(-1 + Sqrt[8 n - 7])/2]
j[n_] := j[n] = d[n] - m[d[n]] (m[d[n]] + 1)/2
Table[k[n], {n, 1, z2}]      (* A205010 *)
Table[j[n], {n, 1, z2}]      (* A205011 *)
Table[s[k[n]], {n, 1, z2}]   (* A205012 *)
Table[s[j[n]], {n, 1, z2}]   (* A205013 *)
Table[s[k[n]] - s[j[n]], {n, 1, z2}]     (* A205014 *)
Table[(s[k[n]] - s[j[n]])/n, {n, 1, z2}] (* A205015 *)