Write the general formula according to the sequence 1,2,5,12,27

Write the general formula according to the sequence 1,2,5,12,27

Let the original sequence be ana1 = 1 A2 = 2 A3 = 5 A4 = 12 A5 = 27a5-a4 = 15 = d4a4-a3 = 7 = d3a3-a2 = 3 = d2a2-a1 = 1 = d1dn = 2 ^ n-1. Add the above formula to obtain an-a1 = D1 + D2 + D3 +... + DN = 2 + 2 ^ 2 +... + 2 ^ N-N = 2 ^ n-1-n, so an = 2 ^ N-N = 1,2,3

Q: (1) 3, 7, 15, 27, 43 （2）21/2,21/4,1/8,-79/16…… （3）3,5,8,12,17,23…… Formula for finding general term
To find the general term formula,

Note: n ^ m is the m power of n
(1)2(n^2)-2n+3
(2)-10+(2n+21)(1\2^N)
(3)(1\2)(4+n+n^2)