Hard to tell without a better look at the stem and blossom end.
I think it might be some sort of Cucurbita maxima squash. If so,
its stem would look more rounded and not so obviously five-sided.
The blossom end might have a bit of a 'button' on it.
C. maxima squashes include hubbard, buttercup, turk's turban
and kabocha types as well as some varieties that are marketed
as 'pumpkins' (including 'white' pumpkins and the Aussie 'blue'
Cushaws, which the other poster mentioned, have a stem end
with five sides and very often the fruit is 'necked' like a butternut.
They generally have a flat, smooth blossom end scar.
Pat in Plymouth MI ('someplace.net' is comcast)
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