Write an explicit formula for the following sequences
1) 4, 7, 12, 19, 28
2) -4, 2, -10, 14, -34
3) 1, -1/2, 1/4, -1/8, 1/16
4) 1, 1, 4/3, 2, 16/5
5) 0, (1-e^1)/(1+e^2), (1-e^2)/(1+e^3), (1-e^3)/(1+e^4), (1-e^4)/(1+e^5)