Number of possibility for a password with the length n and k is the possible number of character :
So I think that n1ckl3b4ck is not so secure
Try password like passphrases type :
alula undress hiccup maison sorry dedicate gombroon shoal kingfish
And you can add some special caracter :
alula!undress#hiccup;Maisonsorry dedicate.gombroon,sh0alkingfish
But don't do thing that are derived from nickelback it can be guessable
Only use random caracter or passphrase with random words choose on different dictionnaries.