In many cases, thinking that we are limited is itself a limiting factor. I've noticed this is true in ever facet of my life. When I was 14, I memorized pi to 50 digits with almost no effort. Later, I memorized it to 100, then 200. I realized at that point that I could memorize anything that I wanted to. I memorize phone numbers, credit card numbers, everything with almost no effort and not using any mnemonic device.…
If you can memorize this without a mnemonic device, then I hate to break it to you, you are a mutant with Eidetic memory. And, so incidentally was your friend.
If you can't, then perhaps you've found a special, easy way to make memorizing numbers easy. Perhaps you should start a website and sell this technique?