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

1,3

Comments

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

Links

Table of n, a(n) for n=1..45.

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).

Crossrefs

Cf. A000982, A258643, A261242.

Sequence in context: A008823 A127719 A074150 * A061925 A073736 A101593

Adjacent sequences: A261240 A261241 A261242 * A261244 A261245 A261246

Keyword

nonn,easy

Author

Wolfdieter Lang, Aug 18 2015

Status

approved