The arithmetic sequence a_ia
i

a, start subscript, i, end subscript is defined by the formula:
a_1 = 5a
1

=5a, start subscript, 1, end subscript, equals, 5
a_i = a_{i - 1} + 2a
i

=a
i−1

+2a, start subscript, i, end subscript, equals, a, start subscript, i, minus, 1, end subscript, plus, 2
Find the sum of the first 700700700 terms in the sequence.