The generator matrix

 1  1  1  1  1  1  1  1  1  1  1  1  1  1  1 X^2  1  1  1  1  1
 0  X  0  X  0 X^2  X X^2+X  0  X X^2 X^2  0 X^2+X X^2+X  X  X  0 X^2 X^2 X^2+X
 0  0  X  X  0  X X^2+X X^2 X^2  X X^2+X X^2  X  0 X^2+X X^2+X  0 X^2  0  X  0
 0  0  0 X^2 X^2 X^2  0 X^2 X^2  0  0  0 X^2  0 X^2 X^2 X^2  0  0  0  0

generates a code of length 21 over Z2[X]/(X^3) who´s minimum homogenous weight is 18.

Homogenous weight enumerator: w(x)=1x^0+31x^18+66x^20+64x^21+62x^22+28x^24+3x^26+1x^40

The gray image is a linear code over GF(2) with n=84, k=8 and d=36.
This code was found by Heurico 1.16 in 0.00398 seconds.