Solves a recurrence equation and returns the value of the requested expression
RSolveValue[eqn, expr, n]
RSolveValue[{eqn1, eqn2, …}, expr, …]
RSolveValue[eqn, expr, {n1, n2, …}]
RSolveValue[{a[n + 1] == 2a[n], a[0] == 1}, a[3], n]
→ 8RSolveValue[a[n + 1] == 3a[n], a[n], n]
→ 3^(-1 + n)*C[1]