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.

1, 1, 2, 3, 6, 9, 14, 19, 26, 33, 42, 51, 62, 73, 86, 99, 114, 129, 146, 163, 182, 201, 222, 243, 266, 289, 314, 339, 366, 393, 422, 451, 482, 513, 546, 579, 614, 649, 686, 723, 762, 801, 842, 883, 926

Offset: 1

Author

Wolfdieter Lang, Aug 18 2015

Keywords

• nonn
• easy

Comments

A shifted version of A061925. - R. J. Mathar, Aug 23 2015

Crossrefs

Cf. A000982, A258643, A261242.

Formula

a(n) = ceiling(((n-2)^2)/2) + 1, n >= 2, a(1) = 1.

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.

O.g.f.: x*(1 - x + x^3 + x^4)/((1-x^2)*(1-x)^2) (from the o.g.f. of A000982).