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 A261243 #8 Aug 23 2015 12:37:26 %S A261243 1,1,2,3,6,9,14,19,26,33,42,51,62,73,86,99,114,129,146,163,182,201, %T A261243 222,243,266,289,314,339,366,393,422,451,482,513,546,579,614,649,686, %U A261243 723,762,801,842,883,926 %N A261243 Row lengths of the irregular triangles A258643 and A261242: maximal number of 0-islands (holes) of certain bisymmetric n X n matrices with 0 or 1 entries only. %C A261243 A shifted version of A061925. - _R. J. Mathar_, Aug 23 2015 %F A261243 a(n) = ceiling(((n-2)^2)/2) + 1, n >= 2, a(1) = 1. %F A261243 a(n) = (1/2)*(n-2)^2+1 if n is even, a(n) = (ceiling((n-2)/2))^2 + (floor((n-2)/2))^2 + 1 if n is odd >= 3, and a(1) = 1. %F A261243 O.g.f.: x*(1 - x + x^3 + x^4)/((1-x^2)*(1-x)^2) (from the o.g.f. of A000982). %Y A261243 Cf. A000982, A258643, A261242. %K A261243 nonn,easy %O A261243 1,3 %A A261243 _Wolfdieter Lang_, Aug 18 2015