David W. answered 11/16/15
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The sequence has a starting value -- f(1)=2.
Then, there are more values, like f(2)=5 and so on.
Now, to go from 2 to 5 allows many possibilities for a "rule," so more values are given. First, look for a "common difference" between the values. Each value given is 3 more than the current value. That rule looks like this:
f(n) = f(n-1) + 3 with f(1)=2
When there is a common difference (the constant value d), we have a rule for an Arithmetic Sequence.
f(n) = f(n-1) + d with f(1)=2 and d=3