The generator matrix

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

generates a code of length 21 over GR(64,4) who´s minimum homogenous weight is 128.

Homogenous weight enumerator: w(x)=1x^0+546x^128+777x^136+3584x^140+742x^144+25088x^148+882x^152+903x^160+245x^168

The gray image is a code over GF(8) with n=168, k=5 and d=128.
This code was found by Heurico 1.16 in 1.23 seconds.