The generator matrix

 1  0  1  1
 0  1 2a^2+3  a

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

Homogenous weight enumerator: w(x)=1x^0+224x^21+28x^24+2240x^28+1568x^29+35x^32

The gray image is a code over GF(8) with n=32, k=4 and d=21.
This code was found by Heurico 1.16 in 0.00013 seconds.