countDigitsNumber _ 0 = 0
countDigitsNumber n a
    | mod a 10 == n = 1 + countDigitsNumber (div a 10) n
    | otherwise = 1 + countDigitsNumber (div a 10) n

countDigits n a b = helper 0 a b
    where
        helper a b sum
            | a == (b + 1) = sum
            | otherwise = helper (a + 1) b (countDigitsNumber a n + sum)


sumDigitRec1 1 = 1
sumDigitRec1 n = sumDigitRec1(div n 10) + mod n 10


sumCountsIter x d
    | not(d >= 0 && d <= 9) = error "Error" -- d > 0 && d < 9 = error "Error" - one more solution, but I think it's better that way