an arithmetic sequence first of all is like
2, 4, 6, 8, 10
where there is a list of numbers in order with an amount added or subtracted to get the next number
here 2 is added
the formula of this is
the first term is a
the n is the nth term of the sequence
the d is the difference between the terms, in this is 2
so the first term is the first number represented by a, or in this instance 2
and the last term is going to be specific to the question as you could add 2 to the sequence forever without an end.
general the last term is commonly scene in what is called an arithmetic series where multiplication and division are used