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 A290984 #42 Jan 21 2023 02:01:32
%S A290984 6,95,427,1828,34619,507629,7342911,21958718,852480872
%N A290984 First n-digit number to appear twice in a row in the decimal expansion of e.
%C A290984 18281828 appears in e before any 1-digit, 2-digit, or 3-digit number appears twice in a row.
%C A290984 a(n) starts at positions 31, 49, 97, 2, 112869, 5005575, 1561314, 69682897, ... - _Bobby Jacobs_, Sep 05 2017
%e A290984 a(1) = 6 because 6 is the first 1-digit number to appear twice in a row in the decimal expansion of e = 2.718281828459045235360287471352(66)...
%t A290984 With[{s = Rest@ First@ RealDigits[N[E, 10^5]]}, Keys@ Merge[#, Identity] &@ Table[TakeSmallest[#, 1] &@ Sort[Map[#[[1, 1]] &, DeleteCases[#, {}]]] &@ Map[SequenceCases[#, {a_, b_} /; b == a + n] &, KeyMap[FromDigits, PositionIndex@ Partition[s, n, 1]]], {n, 4}]] (* _Michael De Vlieger_, Aug 16 2017 *)
%t A290984 (* or *)
%t A290984 s = First@ RealDigits[E,10,51*^5]; Table[p = Partition[s, k, 1]; FromDigits @@ p[[ Select[ Range[ Length@p - k], p[[#]] == p[[#+k]] &, 1]]], {k, 7}] (* much faster, _Giovanni Resta_, Sep 05 2017 *)
%Y A290984 Cf. A001113, A288291, A290977.
%K A290984 base,more,nonn
%O A290984 1,1
%A A290984 _Bobby Jacobs_, Aug 16 2017
%E A290984 a(6)-a(8) from _Giovanni Resta_, Sep 05 2017
%E A290984 a(9) from _Michael S. Branicky_, Jan 20 2023