How do you generate a formula for sequences like 1 ^ 4 +2 ^ 4 +3 ^ 4 + ... + n ^ 4 = n -LRB- 1 + n -RRB- -LRB- 1 +2 n -RRB- -LRB- -1 +3 n +3 n2 -RRB- / 30 ?
7 , 4 , 6 , 3 , 4.5 , 1.5 , 2.25 . What is the next number ?