

A204900


Least k such that n divides s(k)s(j) for some j in [1,k), where s(k) is the kth odd prime.


23



2, 2, 4, 3, 5, 4, 6, 4, 8, 5, 9, 6, 9, 6, 11, 7, 11, 8, 12, 8, 14, 9, 15, 9, 15, 9, 16, 10, 17, 11, 18, 11, 19, 11, 20, 12, 21, 12, 22, 13, 23, 14, 23, 14, 24, 15, 24, 15, 25, 15, 27, 16, 28, 16, 29, 16, 30, 17, 31, 18, 30, 18, 31, 18, 32, 19, 32, 19, 34, 20, 34, 21, 34
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OFFSET

1,1


COMMENTS

See A204892 for a discussion and guide to related sequences


LINKS

Table of n, a(n) for n=1..73.


MATHEMATICA

s[n_] := s[n] = Prime[n + 1]; z1 = 400; z2 = 50;
Table[s[n], {n, 1, 30}] (* A065091 *)
u[m_] := u[m] = Flatten[Table[s[k]  s[j], {k, 2, z1}, {j, 1, k  1}]][[m]]
Table[u[m], {m, 1, z1}] (* A204898 *)
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}] (* A204899 *)
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}] (* A204900 *)
Table[j[n], {n, 1, z2}] (* A204901 *)
Table[s[k[n]], {n, 1, z2}] (* A204902 *)
Table[s[j[n]], {n, 1, z2}] (* A204903 *)
Table[s[k[n]]  s[j[n]], {n, 1, z2}] (* A204904 *)
Table[(s[k[n]]  s[j[n]])/n, {n, 1, z2}] (* A2000034? *)


CROSSREFS

Cf. A000040, A065091, A204892.
Sequence in context: A145393 A215675 A132802 * A070803 A071693 A225381
Adjacent sequences: A204897 A204898 A204899 * A204901 A204902 A204903


KEYWORD

nonn


AUTHOR

Clark Kimberling, Jan 20 2012


STATUS

approved



