\[a_{n+1}=Aa_n+B\]
which use a term to find the succeeding term.Suppose we are to find the rule for the sequence
3, 7, 15, 31, 63, 127,...
As the sequence progresses each term divided by the previous term approaches 2, so we can write
\[a_{n+1}=2a_n+B\]
.\[B\]
is now easily found by considering the first two terms.\[7=2 \times 3 +B \rightarrow B=1\]
The rule is
\[a_{n+1}=2a_n+1\]
.