Tufty Indigo 🪗 on Nostr: npub1vg40c…s2yt8 When you're working mod n, each addition of (n-1) is the same as ...

npub1vg40cghujj2gtg9g5cs7d3x2crvgd80pxc6eklrv95qk2fyaz03q7s2yt8 (npub1vg4…2yt8) When you're working mod n, each addition of (n-1) is the same as subtracting 1, so x*10 ≡ -x (mod 11). Here x is (a*b). The extra 11 on the right-hand side doesn't change the result at all.