The arithmetic sequence a_ia i ​ a, start subscript, i, end subscript is defined by the formula: a_1 = -53a 1 ​ =−53a, start subscript, 1, end subscript, equals, minus, 53 a_i = a_{i - 1} + 6a i ​ =a i−1 ​ +6a, start subscript, i, end subscript, equals, a, start subscript, i, minus, 1, end subscript, plus, 6 Find the sum of the first 880880880 terms in the sequence.