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 A048123 #20 Jun 29 2019 12:32:01
%S A048123 561,1105,10585,101101,1024651,10024561,100427041,1001152801,
%T A048123 10017089857,100023777217,1000151515441,10000879761601,
%U A048123 100000782192961,1000040508690301,10000092861302401,100001371359120001,1000004296444433281,10000011591390633121
%N A048123 Smallest n-digit Carmichael numbers.
%e A048123 a(4)=1105 because 1105 is the smallest 4-digit Carmichael number. [corrected by _Jon E. Schoenfield_, Jan 28 2014]
%t A048123 CarmichaelNbrQ[n_] := ! PrimeQ@ n && Mod[n, CarmichaelLambda@ n] == 1; f[n_] := Block[{k = 10^(n - 1) + 1}, While[! CarmichaelNbrQ@ k, k += 2]; k]; Do[ Print[{n, f[n] // Timing}], {n, 3, 18}]
%Y A048123 Cf. A062568, A062852, A063400.
%K A048123 hard,more,nonn,base
%O A048123 3,1
%A A048123 _Shyam Sunder Gupta_, Feb 17 2002
%E A048123 a(17)-a(20) from _Amiram Eldar_, Jun 29 2019