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A278772
Number of n X 2 0..1 arrays with rows in nondecreasing lexicographic order and columns in nonincreasing lexicographic order, but with exactly two mistakes.
1
0, 2, 20, 117, 503, 1750, 5209, 13751, 33000, 73282, 152581, 300872, 566293, 1023724, 1786462, 3021818, 4971616, 7978746, 12521114, 19254543, 29066411, 43142066, 63046335, 90822745, 129113400, 181302810, 251689347, 345688410, 470071817
OFFSET
1,2
LINKS
FORMULA
Empirical: a(n) = (1/3628800)*n^10 + (1/80640)*n^9 + (1/3780)*n^8 + (17/8064)*n^7 + (1513/172800)*n^6 + (167/11520)*n^5 + (12329/362880)*n^4 + (197/4032)*n^3 - (2167/50400)*n^2 - (11/168)*n.
Conjectures from Colin Barker, Feb 10 2019: (Start)
G.f.: x^2*(2 - 2*x + 7*x^2 - 14*x^3 + 12*x^4 - 5*x^5 + x^6) / (1 - x)^11.
a(n) = 11*a(n-1) - 55*a(n-2) + 165*a(n-3) - 330*a(n-4) + 462*a(n-5) - 462*a(n-6) + 330*a(n-7) - 165*a(n-8) + 55*a(n-9) - 11*a(n-10) + a(n-11) for n>11.
(End)
EXAMPLE
Some solutions for n=4:
..0..0. .0..1. .1..1. .1..1. .1..1. .0..1. .0..1. .0..1. .1..1. .1..0
..0..1. .0..0. .1..0. .1..0. .1..0. .0..0. .1..0. .1..0. .1..1. .0..1
..0..0. .1..0. .1..0. .0..1. .0..0. .0..1. .1..1. .1..1. .1..0. .1..0
..0..1. .1..0. .0..0. .0..1. .1..1. .1..1. .1..0. .0..0. .0..1. .0..0
CROSSREFS
Column 2 of A278778.
Sequence in context: A084894 A203238 A061004 * A213432 A219837 A219759
KEYWORD
nonn
AUTHOR
R. H. Hardin, Nov 28 2016
STATUS
approved