Sundaram sieve

sundaram.rb

# IT REALLY WORKS! CHECK IT AT https://bit.ly/3d9iWIU !

def primes(limit)
	limit /= 2
	t = [true] * limit
	t[0] = false
	i = 0
	k = 1

	while i < limit
		i += k*2 + 2
		j = i
		k += 2
		while j < limit
			t[j] = false
			j += k
		end
	end

	primes = [2]
	t.each_with_index do |prime, index|
		primes << 2*index + 1 if prime
	end

	primes
end

puts primes(100)