a(2) = 18 because 18 is the first 2-digit number to repeat in the decimal expansion of e = 2.7(18)28(18)...
2 appears at positions 0 and 4.
18 appears at positions 2 and 6.
182 appears at positions 2 and 6.
1828 appears at positions 2 and 6.
98793 appears at positions 478 and 494.
987931 appears at positions 478 and 494.
4349076 appears at positions 170 and 2731.
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