Decode number codes to letters using encoding from A Friendly Introduction to Number Theory textbook, with a=11 and z=36

decode.py

import sys

letterdict = {
        11:'a',
        12:'b',
        13:'c',
        14:'d',
        15:'e',
        16:'f',
        17:'g',
        18:'h',
        19:'i',
        20:'j',
        21:'k',
        22:'l',
        23:'m',
        24:'n',
        25:'o',
        26:'p',
        27:'q',
        28:'r',
        29:'s',
        30:'t',
        31:'u',
        32:'v',
        33:'w',
        34:'x',
        35:'y',
        36:'z'
        }

print("Arguments count: "+str(len(sys.argv))) 
print("Please provide arguments in even digit numbers")
for i, arg in enumerate(sys.argv):
    if i>0:
        #print("Argument "+str(i)+": "+arg)
        for i in range(int(len(arg)/2)):
            c1 = arg[2*i]
            c2 = arg[2*i+1]
            ##print("Decoding: "+c1+c2)
            num = (int(c1)*10)+int(c2)
            print(str(letterdict[num]))