//
// program to find and print primes using sieve of Erastosthenes
//
println("enter largest value to check")

val N = readInt

// isPrime(i) will be false if i has been "crossed out" as not prime
val isPrime = Array.fill(N+1)(true)

isPrime(0) = false
isPrime(1) = false

for (i <- 2 to math.ceil(math.sqrt(N)).toInt) {
  if (isPrime(i)) {
    // "cross out" multiples of i
    for (j <- 2*i to N by i) {
      isPrime(j) = false
    }
  }
}

println("primes less than or equal to " + N + ":")
for (i <- 2 to N) {
  if (isPrime(i)) println(i)
}