|
%I #8 Aug 23 2015 12:37:26
%S 1,1,2,3,6,9,14,19,26,33,42,51,62,73,86,99,114,129,146,163,182,201,
%T 222,243,266,289,314,339,366,393,422,451,482,513,546,579,614,649,686,
%U 723,762,801,842,883,926
%N 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 A shifted version of A061925. - _R. J. Mathar_, Aug 23 2015
%F a(n) = ceiling(((n-2)^2)/2) + 1, n >= 2, a(1) = 1.
%F 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 O.g.f.: x*(1 - x + x^3 + x^4)/((1-x^2)*(1-x)^2) (from the o.g.f. of A000982).
%Y Cf. A000982, A258643, A261242.
%K nonn,easy
%O 1,3
%A _Wolfdieter Lang_, Aug 18 2015
|
