F(1)=2,f(n)=f(n-1)+21 for n>2

Question

find the first 4 terms in the sequence 

Answer 1

F(1) = 2 is given 

For any other value you have to know the one before it.  This is not strictly true but based on where you are at in mathematics right now.

For the next value we have F(n)=F(n-1)+21 so for F(2):

F(2) = F(2-1)+21 and F(2-1) = F(1) which we were given so

F(2) = 2+21 = 23

F(3) = F(3-1)+21 and F(3-1) = F(2) so

F(3) = 23+21 = 44 

And I leave the last term and the answer to your other question to you :)

Answer 2

If  f (n) = 2

Then,fn =f (n+1)+21

N=2,f (1) =(2+1)+21

Fn= 24

Therfore sequence  for four is 24,27,30 and 33