Given the sequence {an}, A1 = 1 / 3, the relation between Sn and an is Sn = n multiplied by (2n-1) multiplied by an, the general formula of {an} is obtained

From s [n] - s [n-1] = a [n] (where [n] denotes the subscript n), we can get a [n] = a [n-1] × (2n-3) / (2n + 1) = a [n-2] × (2n-3) × (2n-5) / (2n + 1) = a [n-3] × (2n-3) × (2n-5) × (2n-7) / (2n + 1) / (2n -

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