r = foldr merge [] . map (\n -> map (*n) [1..])

##</code><code>##

merge []     ys = ys
merge xs     [] = xs
merge (x:xs) (y:ys)
    | x < y     = x : merge xs (y:ys)
    | y < x     = y : merge (x:xs) ys
    | otherwise = x : merge xs ys

##</code><code>##

> take 60 (r [2,3,5])
[2,3,4,5,6,8,9,10,12,14,15,16,18,20,21,22,24,25,26,27,28,30,32,33,34,35,36,38,39,40,42,44,45,46,48,50,51,52,54,55,56,57,58,60,62,63,64,65,66,68,69,70,72,74,75,76,78,80,81,82]