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 A230585 #4 Oct 25 2013 16:52:24 %S A230585 3,5,14,42,132,429,1430,4862,16796,58786,208012,742900,2674440, %T A230585 9694845,35357670,129644790,477638700,1767263190,6564120420, %U A230585 24466267020,91482563640,343059613650,1289904147324,4861946401452,18367353072152,69533550916004,263747951750360 %N A230585 First terms of first rows of zigzag matrices as defined in A088961. %C A230585 a(n) = A088961(A056520(n-1)); %C A230585 a(n) = A000108(n+1) for n > 1. %H A230585 Reinhard Zumkeller, <a href="/A230585/b230585.txt">Table of n, a(n) for n = 1..1000</a> %F A230585 a(n) = binomial(2*n,n) - binomial(2*n,n+2) + 0^(n-1). %o A230585 (Haskell) %o A230585 a230585 1 = 3 %o A230585 a230585 n = a007318 (2*n) n - a007318 (2*n) (n+2) %Y A230585 Cf. A007318. %K A230585 nonn %O A230585 1,1 %A A230585 _Reinhard Zumkeller_, Oct 25 2013