I discovered this by accident many years ago when a school I was going to set my login password as my social security number. Besides the fact that it was a very bad idea to use my ssn as a password, I had the number memorized in no time.

Now, if I need to memorize a new bank account number, passport number, or any other important but infrequently used number, I just insert it into a longer passphrase until I have it memorized and then change or make a new passphrase.

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