What does b17 actually stand for?

[Ge0]

Hello there,

I am reading chia's source code (especially chiapos) and I have come accross the b17 symbol but I cannot understand what it does refer to. It's part of the plotting process but have no clue where it comes from.

Any idea?

[lin7sh]

I think it's deprecated version used it Beta17

[Ge0]

Thank you.