770 decimal digits a few days ago, blowing away the previous best by a pretty huge margin.
https://chainz.cryptoid.info/ric/block.dws?793872.htm(Gatra, your idea of having periodic big blocks was awesome. :-)
From a PoW / chain research perspective, it'd be interesting if there was an elegant way of keeping the blockchain growing while work on the record block continued. *ponder* Maybe setting a "big block eligible" flag that gets cleared when the big block is found, but allowing normal-diff blocks to propagate at substantially reduced reward during the big block mining time?
Hm. Probably the easiest would be to allow 5-chains in some way to achieve the reduced diff. One could use a primecoin-style "fractional" amount, or a conventional hash-diff.
The latter is much easier to calibrate...
This is if you want a dense 5-chain, which seems like the most Riecoin-like solution (only look at the first 5 prime spots, ignore the 6th for this purpose):
P(6-chain at difficulty high) ~= 1/ln(hi) ^ 6 (targets 2h instead of 2.5min == 48x harder)
To equalize a 5-chain at high diff to low diff requires:
1/ln(hi) ^5 * frac = 1/ln(hi)^6 / 48
frac = 1 / (48 * ln(hi) )
Then frac just needs to be hash(entire output) has zeros in the first log2(1/frac) bits.
Giving those blocks a tiny block reward should be enough to incent releasing them while they're found incidental to searching for the 6-chain.