A sequence of numbers \(a_1, a_2,a_3,a_4\)... is defined by
\(a_1=1 \cdot 1\)
\(a_2=1 \cdot 2 + 2\cdot1\)
\(a_3=1\cdot3+2\cdot2+4\cdot1\)
\(a_4=1\cdot4+2\cdot3+4\cdot2+8\cdot1\)
...
(a) Use the pattern to write out an expression for \(a_5\), then compute its value.
(b) There is a short formula for \(a_n\) not involving a sum. Use whatever mathematical techniques you know to find or guess the formula.
(c) If you are able to, prove that your formula works for all \(a_n\).
I already got the answers to (a) and (b), I just need help with (c).
The answer to (a) is 57, and the answer to (b) is \(a_n=2^{n+1}-(n+2)\). I just have no idea why this formula works.
PLEASE HELP!!!!! THANKS!!!!
