did you ever find a solution to counting up to such a large number?
i looked i to the problem too. specifically only using the eeprom to store the counter.
but the limits are how often you can toggle a bit = 100K times.
i looked in to balanced gray code, which would turn your counter number in to a bit series. this series of bits will use all the bits equally often.
the problem so far is balanced gray code can not be generated with a simple formula, like regular gray code can.
for balanced gray code you need to store a transition sequence that is basically as long as you counter.
in my case that would be 2^21 x 4 bits. so too big to be stored in the progmem.