function value = prism_unit_monomial_integral ( expon )

%*****************************************************************************80
%
%% prism_unit_monomial_integral(): monomial integral in a unit prism.
%
%  Discussion:
%
%    This routine returns the integral of
%
%      product ( 1 <= I <= 3 ) X(I)^EXPON(I)
%
%    over the unit triangular prism.
%
%    A unit triangular prism has a triangular base in the (x,y) plane,
%    projected vertically one unit in the z direction.  
%
%    The vertices are 
%      (1,0,0), (0,1,0), (0,0,0), 
%      (1,0,1), (0,1,1), (0,0,1), 
%
%  Licensing:
%
%    This code is distributed under the MIT license.
%
%  Modified:
%
%    17 May 2023
%
%  Author:
%
%    John Burkardt
%
%  Input:
%
%    integer EXPON(3): the exponents.
%
%  Output:
%
%    real VALUE: the integral of the monomial.
%
  value =  factorial ( expon(1) ) ...
        * factorial ( expon(2) ) ...
        / ( expon(3) + 1 ) ...
        / factorial ( expon(1) + expon(2) + 2 );

  return
end
