val hamming = 1 # merge( map((2*), hamming), merge(map((3*), hamming), map((5*), hamming)) )

def
  merge( inx@x:_, iny@y:_ )
    | x < y     = x # merge( inx.tail(), iny )
    | x > y     = y # merge( inx, iny.tail() )
    | otherwise = merge( inx, iny.tail() )

println( hamming.take(20) )
println( hamming(1690) )
println( hamming(2000) )