score :: Int -> Integer
score = floor . rationalPart . binet
 where
  binet n = (φ ^ n - recip φ ^ n) / sqrt5
  φ     = (1 + sqrt5) / 2
  sqrt5 = Q5 0 1

m
score :: Int -> Integer
score = floor . rationalPart . binet
 where
  binet n = (φ ^ n - recip φ ^ n) / sqrt5
  φ     = (1 + sqrt5) / 2
  sqrt5 = Q5 0 1
score = floor . rationalPart . binet
 where
  binet n = (φ ^ n - recip φ ^ n) / sqrt5
  φ     = (1 + sqrt5) / 2
  sqrt5 = Q5 0 1