Noted security researcher MC Frontalot claims that one simply can’t hide secrets from the future with math, although you can try. Maybe he’s right.
One trick for making up long, complicated, but easy-to-remember passwords is to use a (fake) email address. This gives a long password a familiar mnemonic structure which can lend itself very naturally to a larger mnemonic scheme. The password even includes a few non-alphanumerics (@ and .) pretty much for free, as far as human memory consumption goes.
"WinstonSmith@Room101.com," for example, gets top scores on the GeekWisdom and Microsoft password testers. It’s much too long for currently-practical rainbow tables to work on. But its pretty easy to remember, and its a lot easier to type than the line-noise a random password generator puts out.