In Exercises 19–22, the general term of a sequence is given and involves a factorial. Write the first four terms of each sequence. a_n=(n+1)!/n^2

Evaluate the expression.

$\frac{12}{4!}$

Evaluate the expression.

$\frac{9!}{7!}$

Evaluate the expression.

$\frac{16!}{12!\cdot 4!}$

Write the first 4 terms of the sequence $a_n=n^2\cdot (n-1)!$

In Exercises 19–22, the general term of a sequence is given and involves a factorial. Write the first four terms of each sequence. a_n=−2(n−1)!

In Exercises 23–28, evaluate each factorial expression. 18!/16!

In Exercises 23–28, evaluate each factorial expression. 20!/2!18!

In Exercises 23–28, evaluate each factorial expression. (2n+1)!/(2n)!