Sam is comparing the half-life of two isotopes of uranium. The half-life of Uranium-238 is 4.5 times 10^9 years. The half-life of Uranium-233 is 1.6 times 10^5 years. He computed how much greater the half-life of Uranium-238 is than that of Uranium-233, and his calculator displayed the number 2.81E4. What is this number in scientific notation?