A189894 Number of isosceles right triangles on a 2n X (n+1) grid.
4, 50, 208, 582, 1308, 2556, 4528, 7460, 11620, 17310, 24864, 34650, 47068, 62552, 81568, 104616, 132228, 164970, 203440, 248270, 300124, 359700, 427728, 504972, 592228, 690326, 800128, 922530, 1058460, 1208880, 1374784, 1557200, 1757188
Offset: 1
Keywords
Examples
Some solutions for n=2 ..0..0....2..2....2..1....1..1....0..2....3..2....3..0....2..0....0..1....1..0 ..0..1....2..1....2..2....0..0....0..0....2..2....2..0....1..1....1..0....0..2 ..1..0....3..2....3..1....0..2....2..2....3..1....3..1....3..1....1..2....3..1
Links
- R. H. Hardin, Table of n, a(n) for n = 1..71
Crossrefs
Cf. A189895.
Formula
Empirical: a(n) = 4*a(n-1) -5*a(n-2) +5*a(n-4) -4*a(n-5) +a(n-6).
Empirical: a(n) = -1/16 +11*n^4/8 +7*n^3/2 +3*n^2/4 -3*n/2 +(-1)^n/16 with g.f. -2*x*(2+17*x+14*x^2)/ ((1+x)*(x-1)^5). - R. J. Mathar, May 18 2011
Comments