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 A063400 #15 Jun 29 2019 12:32:07
%S A063400 561,8911,75361,997633,9890881,99861985,993905641,9999109081,
%T A063400 99976607641,999629786233,9999501351841,99994742993377,
%U A063400 999922265173441,9999924433632001,99999201310035841,999996386511276505,9999998594193164041
%N A063400 Largest n-digit Carmichael numbers.
%e A063400 a(4)=8911 because 8911 is the largest 4-digit Carmichael number. [corrected by _Jon E. Schoenfield_, Jan 28 2014]
%t A063400 CarmichaelNbrQ[n_] := !PrimeQ[n] && Mod[n, CarmichaelLambda[n]] == 1; f[n_] := f[n] = Block[{k = 10^n - 1}, While[!CarmichaelNbrQ[k], k -= 2]; k]; Reap[Do[Print[{n, f[n]}]; Sow[f[n]], {n, 3, 10}]][[2, 1]] (* _Jean-François Alcover_, Jan 28 2014, after _Shyam Sunder Gupta_ *)
%Y A063400 Cf. A062568, A062852, A048123.
%K A063400 hard,more,nonn,base
%O A063400 3,1
%A A063400 _Shyam Sunder Gupta_, Feb 17 2002
%E A063400 a(17)-a(19) from _Amiram Eldar_, Jun 29 2019