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 A297829 #4 Feb 06 2018 19:27:12
%S A297829 51,59,243,279,287,295,363,371,422,430,538,587,684,872,934,1075,1083,
%T A297829 1091,1232,1268,1304,1312,1320,1388,1396,1515,1598,1634,1642,1650,
%U A297829 1718,1726,1855,1891,1899,1907,1975,1983,2034,2042,2093,2101,2209,2258,2355,2363
%N A297829 Duplicates in A297826.
%t A297829 mex[list_, start_] := (NestWhile[# + 1 &, start, MemberQ[list, #] &]);
%t A297829 tbl = {}; a[0] = 1; a[1] = 2; b[0] = 3; b[1] = 4;
%t A297829 a[n_] := a[n] = a[1]*b[n - 1] - a[0]*b[n - 2] + n;
%t A297829 b[n_] := b[n] = mex[tbl = Join[{a[n], a[n - 1], b[n - 1]}, tbl], b[n - 1]];
%t A297829 du = Differences[Table[a[n], {n, 0, 1000}]] (* A297827 *)
%t A297829 w = Flatten[Position[du, 0]]; Map[a, w] (* A297829 *)
%Y A297829 Cf. A297826.
%K A297829 nonn,easy
%O A297829 1,1
%A A297829 _Clark Kimberling_, Feb 04 2018