This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A288291 #40 Jan 21 2023 02:00:29
%S A288291 31,49,97,2,112869,5005575,1561314,69682897,1841794338
%N A288291 Position of the first time an n-digit number appears twice in a row after the decimal point of e.
%C A288291 18281828 appears in e before any 1-digit, 2-digit, or 3-digit number appears twice in a row.
%e A288291 a(1) = 31 because the first time a 1-digit number appears twice in a row in the decimal expansion of e is 31 digits after the decimal point: 2.718281828459045235360287471352(66)...
%t A288291 s = First@ RealDigits[E, 10, 51*^5]; Table[p = Partition[s, k, 1];
%t A288291 SelectFirst[ Range[ Length[p] - k], p[[#]] == p[[# + k]] &] - 1, {k, 7}] (* _Giovanni Resta_, Sep 05 2017 *)
%Y A288291 Cf. A001113, A287994, A290984.
%K A288291 nonn,base,more
%O A288291 1,1
%A A288291 _Bobby Jacobs_, Sep 01 2017
%E A288291 a(6)-a(8) from _Giovanni Resta_, Sep 05 2017
%E A288291 a(9) from _Michael S. Branicky_, Jan 20 2023