describe do
it do
2.prime?.should be_true
3.prime?.should be_true
(2**31-1).prime?.should be_true # 8th Mersenne prime (M8)
end
it do
4.prime?.should be_false
15.prime?.should be_false
(2**32-1).prime?.should be_false
( (2**17-1)*(2**19-1) ).prime?.should be_false # M6*M7
end
end