I had a quick look, I think it's a great first try. Here are my thoughts!
module DivRusse where
{-
Comments:
* This seems unsafe in that it doesn't handle negative numbers well.
* This can be evidenced by needing a guard on our property.
* Could be addressed by using a safe newtype.
* Define properties and use quickcheck to test them.
* Favor pattern-matching over use of `fst`, `snd`.
* Use `where` over `let` to highlight what the final result is.
* Rewrite folds to more wholemeal approach. e.g. `sum $ map snd filteredPair`
* Use standard functions and composition to eliminate lambdas like this: `(\(x, _) -> x `mod` 2 /= 0 )` = `(odd . fst)`.
* `russmulList` could go into an infinite loop for negative numbers. Either prevent this with types (preferred), or return an error somehow.
-}
main :: IO ()
main = do
putStrLn "13 x 12 is"
print $ russmul 13 12
-- Property: Does russmul = *?
prop_russmul :: Int -> Int -> Bool
prop_russmul a b
| a > 0 && b > 0 = russmul a b == a * b
| otherwise = True
russmul :: Int -> Int -> Int
russmul a b = sum $ map snd filteredPair
where
filteredPair = filter (odd . fst) $ (a,b) : russmulList a b
russmulList :: Int -> Int -> [(Int, Int)]
russmulList 1 _ = []
russmulList a b = (a', b') : russmulList a' b'
where
a' = a `div` 2
b' = b * 2