1,1

The first two occurrences of a(4) = 1828 appear consecutively as 18281828.

Table of n, a(n) for n=1..12.

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.

...

Cf. A001113, A197123.

Sequence in context: A019581 A183285 A129627 * A138413 A066274 A052623

Adjacent sequences: A279857 A279858 A279859 * A279861 A279862 A279863

nonn,base,more

Bobby Jacobs, Dec 20 2016

a(8)-a(12) from Alois P. Heinz, Dec 21 2016

approved