open System.Numerics

​

let c = 244712744540788243I

​

let rec coll c n =

    if c = 1I then n

    elif c &&& 1I = 0I

    then coll (c >>> 1) (n + 1)

    else coll ((c * 3I) + 1I) (n + 1)

​

​

coll c 0

|> printfn "%A"

​