Thankyou !
Well it seems we will know eventually if there are any more 21 but no 20 grids.
And excellent computation with the double bands .....i knew it was big
I remember a contributor computing the 5e9 grids row by row, but i have failed to locate where it was in the forum - so we could confirm your calculation if it could be located
And its such a shame [ for me ] that the MC grid does have double band with 12 clues .....I will have to edit accordingly !
If there are any double bands which need 13 clues to complete they would surely be in the known grids with bands needing 6 clues.... and we know the status of these grids anyway.