A004784 Numbers k such that 4!*(2k-5)!/(k!*(k-1)!) is an integer.

3, 4, 5, 211, 461, 562, 947, 990, 991, 1223, 1378, 1458, 1600, 1892, 2015, 2069, 2147, 2185, 2333, 2480, 2481, 2666, 2994, 3011, 3017, 3356, 3418, 3433, 3442, 3478, 3479, 3485, 3521, 3554, 3566, 3571, 3620, 3628, 3725, 3809, 3997, 4090, 4096

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Maple

R:= 3: q:= 4!*(2*3-5)!/(3! * 2!): count:= 1:
for n from 4 while count < 100 do
  q:= q*(2*n-5)*(2*n-6)/(n*(n-1));
  if q::integer then
      R:= R, n; count:= count+1;
  fi;
od:
R; # Robert Israel, May 01 2025

Mathematica

Select[Range[16^3], IntegerQ[4! (2 # - 5)!/(#! (# - 1)!)] &] (* Arkadiusz Wesolowski, Sep 06 2011 *)

Crossrefs

Sequence in context: A163483 A327876 A363477 * A338056 A321404 A024687

Adjacent sequences: A004781 A004782 A004783 * A004785 A004786 A004787

Keyword

nonn

Author

R. K. Guy

Extensions

Offset corrected and 2 initial terms added by Arkadiusz Wesolowski, Sep 06 2011

Status

approved