A331881 a(n) is the first n-digit substring to occur n times in the decimal expansion of the fractional part of Pi.
1, 26, 446, 2796, 86538, 872117, 1591292, 66416662
Offset: 1
Examples
a(1) = 1, because '1' is the first 1-digit string appearing 1 time (at position 1); a(2) = 26, because '26' is the first 2-digit string appearing 2 times (at positions 6 and 21); a(3) = 446, because '446' is the first 3-digit string appearing 3 times (at positions 125, 182 and 217); and so on.