Compiler does not like this (but ic you change the size of the static array, it's cool with it)

357.cr

# $ crystal build 357.cr --release
struct SeiveSlot
  property number, divisors

  def initialize(@number : Int32)
    @divisors = [] of Int32
  end

  def prime?
    @divisors.size == 2 && @divisors[0] == 1 && @divisors[1] == @number
  end

  def <<(divisor : Int32) : SeiveSlot
    @divisors.push divisor
    self
  end

  def prime_generator?(seive)
    @divisors.all? do |divisor|
      generated = divisor + @number/divisor
      seive[generated-1].prime?
    end
  end
end

seive = StaticArray(SeiveSlot, 100_000_000).new { |i| SeiveSlot.new i+1 }
puts "allocated"

seive.each do |slot|
  divisor = slot.number
  p "seive: #{divisor}" if divisor % 100_000 == 0
  multiplier = 1
  loop do
    multiple = divisor*multiplier
    break if seive.size < multiple
    seive[multiple-1] << divisor
    multiplier += 1
  end
end

seive.each do |slot|
  next if seive.size <= slot.number
  p slot.number if slot.prime_generator? seive
end