Find a few first Mersenne numbers

mersenne2.fs

let inline mersenne (i: int) =     
    if i = 2 || (isPrime (bigint i) && lucasLehmer i) then
        let p = 1I <<< i
        Some (i, (p/2I) * (p-1I))
    else None

let runPerfectsSeq n =
    seq {1..n}
        |> Seq.choose mersenne
        |> Seq.toArray
    
let runPerfectsPSeq n =
    seq {1..n}
        |> PSeq.choose mersenne
        |> PSeq.sort
        |> PSeq.toArray