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 A111802 #15 Sep 04 2018 12:30:21
%S A111802 1,2,3,11,19,29,41,55,71,89,109,131,155,181,209,239,271,305,341,379,
%T A111802 419,461,505,551,599,649,701,755,811,869,929,991,1055,1121,1189,1259,
%U A111802 1331,1405,1481,1559,1639,1721,1805,1891,1979,2069,2161,2255,2351,2449,2549
%N A111802 n^2-n-1 for n>3; a(1)=1; a(2)=2; a(3)=3.
%C A111802 Inspired by attempt to determine what incorrectly-named A000519 may really be. Conjecture: Sequence is number of different main-diagonal sums among Latin squares of order n. Confirmed for first five terms. Guaranteed to be an upper bound as the diagonal sum can only be in the range from n to n^2 inclusive and it is impossible for the sum to be n+1 or n^2-1. There is probably an easy proof that all other sums in this interval can be realized as the only restriction seems to be that it is not permissible for exactly n-1 numbers on a diagonal to be identical.
%H A111802 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).
%F A111802 a(n) = n^2-n-1 = A028387(n-2) for n>3; a(n) = n for 1<=n<=3.
%e A111802 a(3) = 3, the number of different diagonal sums of all order 3 Latin squares. Their diagonal sums can only be 3, 6 and 9.
%t A111802 Table[If[n<4,n,n^2-n-1],{n,60}] (* or *) LinearRecurrence[{3,-3,1},{1,2,3,11,19,29},60] (* _Harvey P. Dale_, Sep 04 2018 *)
%o A111802 (PARI) a(n)=if(n>3,n^2-n-1,n) \\ _Charles R Greathouse IV_, Dec 20 2011
%Y A111802 Cf. A028387.
%K A111802 nonn,easy
%O A111802 1,2
%A A111802 _Rick L. Shepherd_, Aug 17 2005