6 lines
571 B
FSharp
6 lines
571 B
FSharp
// Circular primes - Nigel Galloway: September 13th., 2021
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let fG n g=let rec fG y=if y=g then true else if y>g && isPrime y then fG(10*(y%n)+y/n) else false in fG(10*(g%n)+g/n)
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let rec fN g l=seq{let g=[for n in g do for g in [1;3;7;9] do let g=n*10+g in yield g] in yield! g|>List.filter(fun n->isPrime n && fG l n); yield! fN g (l*10)}
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let circP()=seq{yield! [2;3;5;7]; yield! fN [1;3;7;9] 10}
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circP()|> Seq.take 19 |>Seq.iter(printf "%d "); printfn ""
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printf "The first 5 repunit primes are "; rUnitP(10)|>Seq.take 5|>Seq.iter(fun n->printf $"R(%d{n}) "); printfn ""
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