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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.
2
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
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
KEYWORD
nonn,easy
AUTHOR
Wolfdieter Lang, Aug 18 2015
STATUS
approved