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 A137823 #4 Jun 16 2016 23:27:35 %S A137823 1,2,3,7,8,21,61,62,183,547,548,1641,4921,4922,14763,44287,44288, %T A137823 132861,398581,398582,1195743,3587227,3587228,10761681,32285041, %U A137823 32285042,96855123,290565367,290565368,871696101,2615088301,2615088302 %N A137823 Numbers occurring in A137822 : first differences of numbers n such that 3 | sum( Catalan(k), k=1..2n). %C A137823 This sequence consists of A122983 (which are record values of A137822, i.e. record gaps of A137821), plus the successor of every other term thereof (i.e. A122983(2k+1)+1). See A137822 for more details & formulas. %C A137823 The (very simple) sequence A137824 gives the index of A137822 at which A137823(n) occurs for the first time. %o A137823 (PARI) A137823(n) = (n%3==2)+3^((n-1)*2\3+1)\4+1 %Y A137823 Cf. A107755, A122983, A137821-A137824. %K A137823 nonn,easy %O A137823 1,2 %A A137823 _M. F. Hasler_, May 15 2008