A111869 - OEIS

A111869

Least number k such that C(2k,k) is divisible by n^2.

1, 3, 5, 15, 13, 5, 25, 63, 41, 13, 61, 15, 85, 25, 14, 255, 145, 41, 181, 23, 25, 61, 265, 95, 313, 85, 365, 27, 421, 14, 481, 1023, 61, 145, 39, 53, 685, 181, 86, 63, 841, 25, 925, 61, 44, 265, 1105, 383, 1201, 313, 145, 85, 1405, 365, 63, 95, 181, 421, 1741, 23, 1861

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

Seiichi Manyama, Table of n, a(n) for n = 1..500

MATHEMATICA

f[n_] := Block[{k = 1, m = n^2}, While[ Mod[ Binomial[2k, k], m] != 0, k++ ]; k]; Array[f, 61]

CROSSREFS

Cf. A000984, A059097, A073078.

Sequence in context: A160046 A349553 A272024 * A093015 A371450 A243940

Adjacent sequences: A111866 A111867 A111868 * A111870 A111871 A111872

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Nov 23 2005

STATUS

approved