A225976 Number of n X 2 binary arrays whose sum with another n X 2 binary array containing no more than two 1s has rows and columns in lexicographically nondecreasing order.

4, 15, 48, 138, 350, 790, 1616, 3049, 5384, 9001, 14376, 22092, 32850, 47480, 66952, 92387, 125068, 166451, 218176, 282078, 360198, 454794, 568352, 703597, 863504, 1051309, 1270520, 1524928, 1818618, 2155980, 2541720, 2980871, 3478804, 4041239

Offset

1,1

Links

R. H. Hardin, Table of n, a(n) for n = 1..210

Formula

Empirical: a(n) = (11/120)*n^5 - (1/8)*n^4 + (9/8)*n^3 - (7/8)*n^2 + (287/60)*n - 1.

Conjectures from Colin Barker, Sep 05 2018: (Start)

G.f.: x*(4 - 9*x + 18*x^2 - 5*x^3 + 2*x^4 + x^5) / (1 - x)^6.

a(n) = 6*a(n-1) - 15*a(n-2) + 20*a(n-3) - 15*a(n-4) + 6*a(n-5) - a(n-6) for n>6.

(End)

Example

Some solutions for n=3:
..0..1....1..1....0..0....0..0....1..1....0..1....0..0....0..1....1..1....0..1
..0..0....1..1....1..1....0..1....1..0....0..1....0..1....0..1....0..0....0..1
..1..1....0..1....0..0....1..1....1..0....0..1....0..0....1..0....1..1....1..1

Crossrefs

Column 2 of A225982.

Sequence in context: A238807 A240333 A227099 * A093967 A052201 A320460

Adjacent sequences: A225973 A225974 A225975 * A225977 A225978 A225979

Keyword

nonn

Author

R. H. Hardin, May 22 2013

Status

approved