Today I've succesfully generated a seed for a Nano/xrb address with a special set of starting characters:
Account: xrb_1nano... Seed: 0B3D56CB4BB15AE3912AD4CF05F0BD7E791DBD5B9AAE70BFF7BA9DF55621D436
With this seedphrase the 0 index private key generated will be the one displayed above.
Before I found an address that matched the first 4 characters in the public-key, I had to randomly generate 2 million + seed/private keys which took a few minutes of processing with a GPU (could take up to an hour with a CPU). You can imagine that finding an address with 5 or 6 characters predefined will get a lot more computationally intensive, but image what type of processing power or luck you need to guess (brute force) the seed for a full wallet address at a length of 59 characters... It will take more time than the age of the universe, even with all the computing power in the solar system!
Just for fun I sent a penny to it, the first reader to be able to enter the seed in his/her wallet get the prize! Check who won on the blockchain explorer:
I want to thank Github user Lee Bousfield (PlasmaPower) for coding this wonderfull Vanity address generator with GPU support, it would have taken me hours otherwise :')
Remember to protect your seedphrase/private key with your life, because once you post it online someone else will win the lottery of spending your hard earned Nano!