The number of patterns to match is small, so you can set up a list of regular expressions to capture this. For example, for five digit sequences:

grep -e 12345 -e 23456 […] -e 65432 -e 54321

Many big files indicate that this needs to be done quickly. That means a while read loop is out of the question. One thing to realize here is that each of these exercises can be simplified into matching (at least) one of a small set of patterns, and this can be done really fast using grep or similar tools like rg or ack. For example, for five digit sequences:

grep -e 12345 -e 23456 […] -e 65432 -e 54321

See man grep for more information, and use Greg's Wiki to learn Bash quickly.