To get the arithmetic sequence, you should get the firts time (Asub1), the last term (AsubN) the number of terms (n) and most specially the common difference (d). To get the next term of the previous term, you should get first the common difference. getting the common defference is by subtracting the First term (Asub1) and the second term (Asub2). example, 10(Asub1)+20(Asub2)+30(Asub3),_,_,_ ~20-(Asub2)10(Asub1)=10. then if you're still not satiesfied to get the common, go on to the another term. Subtract the third term (Asub3) and the second term(Asub) so 30(Asub3)-20(Asub1)=10. The answer in subtracting Asub2 minus Asub1 is equal to the answer of Asub3 minus Asub2. So, the common difference now is 10 (which is the answer of the term who got subtracted). How to get the next term? in my example, 10+20+30,_,_,_. Just add the common difference from the last term. Example: the last term is 30. so 30+10=40. so the next term is 40 and justy repeat the cycle.