A004786 - OEIS

A004786

Numbers k such that 6!*(2*k-7)!/(k!*(k-1)!) is an integer.

4, 6, 7, 991, 2481, 3479, 6163, 6581, 8178, 8179, 9272, 10288, 12195, 13067, 13976, 15199, 15813, 16172, 18371, 18686, 18723, 18747, 19294, 19438, 19506, 23531, 26198, 26315, 26678, 27877, 28429, 30553, 30593, 30689, 31327, 31375, 32882, 33006, 33451

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OFFSET

1,1

LINKS

Robert Israel, Table of n, a(n) for n = 1..1000

MAPLE

R:= 4: q:= 6!*(2*4-7)!/(4! * 3!): count:= 1:

for n from 5 while count < 100 do

q:= q*(2*n-7)*(2*n-8)/(n*(n-1));

if q::integer then

R:= R, n; count:= count+1;

fi;

od:

R; # Robert Israel, May 01 2025

MATHEMATICA

Select[Range[10^4], IntegerQ[6! (2 # - 7)!/(#! (# - 1)!)] &] (* Arkadiusz Wesolowski, Sep 06 2011 *)

CROSSREFS

Sequence in context: A012760 A333742 A107648 * A263357 A394006 A195387

Adjacent sequences: A004783 A004784 A004785 * A004787 A004788 A004789

KEYWORD

nonn

AUTHOR

R. K. Guy

EXTENSIONS

More terms from David W. Wilson, Dec 11 1999

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

STATUS

approved