What comes next in series 31353213?

How many feet in 600 squre feet? What is two thirds f 27? What is the contribution of Georg Joachim Iserin in trigonometry? What are some examples of analogous term proportionality? What number is greater then the number expressed by 3.4 10101010101010? What is 2.0x10 to the negative third power? How many jars will you need for a thousand pennies? How many faces does a triangular based pyrimid have? What remainders are possible when you divide a number by 6? Why we use o'clock after time? What of these applies to form? What is 0.125 rounded to the nerest thousadths? Is NF3 a trigonal pyramidal? How do you write 8.91 into a percent? What is the 5ft dimension in meters? How mant months in a year? X to the 2nd power plus 2x equals 12? What is 20percent off of 50 dollars? What is 0.08 written as a fraction and in simplest form? What does 206b in your b mean?