The generator matrix

 1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1
 0  2  0  0  0  2  0 2a 2a  2 2a+2 2a+2  2 2a  2 2a+2  0  0
 0  0  2  0  0 2a+2  2  0 2a 2a 2a  2 2a  0 2a+2  0 2a+2  0
 0  0  0  2  0  2 2a+2 2a+2 2a  0 2a  2  0  2 2a  2 2a  0
 0  0  0  0  2 2a+2 2a  2 2a+2  2  0  2 2a  2 2a 2a+2 2a  0

generates a code of length 18 over GR(16,4) who´s minimum homogenous weight is 40.

Homogenous weight enumerator: w(x)=1x^0+54x^40+120x^44+156x^48+180x^52+3072x^54+180x^56+144x^60+147x^64+36x^68+6x^72

The gray image is a code over GF(4) with n=72, k=6 and d=40.
This code was found by Heurico 1.16 in 0.0341 seconds.