c1 sequences and series

Im having problems with chapter 6 of c1 sequences and series is there anyone who can help

Post some examples of questions from topics that you're struggling with and your working out for those questions

question 1:
suggest possible recurrence relationships for the following sequences,
1: 3,5,7,9,......
2: 100,25,6.25,1.5625,......
3: 4,10,18,38,74,.....

question 2:
find the first four terms of the following recurrence relationships,
1: Un+1=(Un)^2-1, U1=2
2: Un+1=Un/2, U1=10
3: Un+2=(2Un+1)+Un, U1=3, U2=5