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 A232898 #19 Jan 04 2018 11:55:40
%S A232898 1,2,7,5,10,12,9,24,31,22,59,25,27,30,42,56,123,66,57,72,84,78,73,132,
%T A232898 136,57,99,80,129,211,170,226,121,170,126,129,238,218,157,132,348,198,
%U A232898 388,103,171,166,247,181,205,352,194,136,430,226,117,224,237,292,364,241
%N A232898 Least positive integer m such that {C(2k,k) + k: k = 1,...,m} contains a complete system of residues modulo n, or 0 if such a number m does not exist.
%C A232898 Conjecture: (i) Let n be any positive integer. Then 0 < a(n) <= n^2/2 + 3. Also, {C(2k,k) - k: k = 1, ..., [n^2/2] + 15} contains a complete system of residues modulo n, where [.] is the floor function.
%C A232898 (ii) For any integer n > 2, neither C(2n,n) + n nor C(2n,n) - n has the form x^m with m > 1.
%H A232898 Chai Wah Wu, <a href="/A232898/b232898.txt">Table of n, a(n) for n = 1..10000</a> (n = 1..250 from Zhi-Wei Sun)
%e A232898 a(2) = 2 since C(2*1,1) + 1 = 3 is odd and C(2*2,2) + 2 = 8 is even.
%t A232898 L[m_,n_]:=Length[Union[Table[Mod[Binomial[2k,k]+k,n],{k,1,m}]]]
%t A232898 Do[Do[If[L[m,n]==n,Print[n," ",m];Goto[aa]],{m,1,n^2/2+3}];
%t A232898 Print[n," ",counterexample];Label[aa];Continue,{n,1,60}]
%Y A232898 Cf. A000984, A232616, A232862, A232894.
%K A232898 nonn
%O A232898 1,2
%A A232898 _Zhi-Wei Sun_, Dec 02 2013