Chapter 5 - Logarithmic, Exponential, and Other Transcendental Functions - 5.4 Exercises - Page 354: 90

$15!=1307674368000$ By Stirling's formula: $15!\approx1300430722199$

$\ 15! = 15\times 14\times 13\times 12 \times 11 \times 10 \times 9 \times 8 \times 7 \times 6 \times 5 \times 4 \times 3 \times 2 \times 1$ Or, $\ 15! = 1307674368000$ Stirling's Formula: $\ 15! \approx \left(\frac{15}{e}\right)^{15} \sqrt{2\pi(15)} = 1300430722199$