The area of a triangle equals base times height times this value, which is also the probability that a fair coin will land on heads.
If p is a Mersenne prime, then p times the quantity "p plus one" times this number yields a perfect number. Evaluating the gamma function at this value yields pi raised to this number, which is the constant of proportionality in the Shoelace Theorem for finding the area of a polygon. This number is conjectured to be the real part of any non-trivial zero of the (*) Riemann zeta function, and taking the square root of a number x equals raising x to the power of this number. The area of a triangle equals base times height times this value, which is also the probability that a fair coin will land on heads. For ten points, identify this fractional value that can be doubled to equal one.
If p is a Mersenne prime, then p times the quantity "p plus one" times this number yields a perfect number.
one-half [accept equivalents like 1/2, 0.5, etc]