GBCode_[[18, 2, 5]]: 
L = 9
a_x = "x + 1"
b_x = "x^8 + x^4"

GBCode_[[36, 2, 6]]: 
L = 18
a_x = "x^13 + x^12"
b_x = "x^12 + x^7"

GBCode_[[30, 2, 5]]: 
L = 15
a_x = "x^9 + x^6"
b_x = "x^12 + x^2"