Assume an SRAM PUF with N words and each word has B bits. How many unique challenges are available for

$1.$ One word is chosen as the response.

$2.$ Two words are used where ORDER of choices is important and no repeated words are allowed in a challenge

$3.$ Three words are used where no repeated words are allowed and order of selection is important

$4.$ One word is chosen but one permutation of the resulting B$-$bit word is chosen