In the equal ratio sequence, Sn is the sum of the first n terms, Sn = 2an-1, and an is obtained An = 2 (n-1) (n-1 power of 2)

In the equal ratio sequence, Sn is the sum of the first n terms, Sn = 2an-1, and an is obtained An = 2 (n-1) (n-1 power of 2)

It is known that Sn = 2an-1
If n = 1, S1 = 2a1-1
And because S1 = A1, we can get A1 = 1 by solving the above equation
Sn=2An-1
S (n-1) = 2A (n-1) - 1 note: "n-1" is subscript
By subtracting the above and the following two expressions:
Sn-S(n-1)=2An-2A(n-1)
That is, an = 2an-2a (n-1)
Arrangement: an / a (n-1) = 2
So {an} is an equal ratio sequence with 1 as the first term and 2 as the common ratio
That is, an = 2 ^ (n-1)