Long primes: Difference between revisions
→{{header|Scala}}
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</pre>
=={{header|Scala}}==
<lang scala>object LongPrimes extends App {
def primeStream = LazyList.from(3, 2)
.filter(p => (3 to math.sqrt(p).ceil.toInt by 2).forall(p % _ > 0))
def longPeriod(p: Int): Boolean = {
val mstart = 10 % p
@annotation.tailrec
def iter(mod: Int, period: Int): Int = {
val mod1 = (10 * mod) % p
if (mod1 == mstart || period >= p) period
else iter(mod1, period + 1)
}
iter(mstart, 1) == p - 1
}
val longPrimes = primeStream.filter(longPeriod(_))
println("long primes up to 500:")
println(longPrimes.takeWhile(_ <= 500).mkString(" "))
println
val limitList = Seq.tabulate(8)(math.pow(2, _).toInt * 500)
for (limit <- limitList) {
val count = longPrimes.takeWhile(_ <= limit).length
println(f"there are $count%4d long primes up to $limit%5d")
}
}
</lang>
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