login
A303295
a(n) is the maximum water retention of a height-3 length-n number parallelogram with maximum water area.
3
0, 20, 49, 99, 165, 247, 345, 459, 589, 735, 897, 1075, 1269, 1479, 1705, 1947, 2205, 2479, 2769, 3075, 3397, 3735, 4089, 4459, 4845, 5247, 5665, 6099, 6549, 7015, 7497, 7995, 8509, 9039, 9585, 10147, 10725, 11319, 11929, 12555
OFFSET
0,2
COMMENTS
A number parallelogram contains numbers from 1 to the triangular area of the parallelogram without duplicate numbers.
This sequence applies the water retention model for mathematical surfaces to the triangular grid.
Magic polyiamond tiling is the tiling of a number shape with a single order of polyiamond. The sum of numbers in each polyiamond subspace is equal.
The height-three length-four parallelogram has an area of 24 unit triangles. The sum of the numbers from 1 to 24 is 300. Both 24 and 300 are divisible by four and six making magic polyiamond tilings possible with order four and six polyiamonds.
Five magic polyiamond tilings for a single numeric solution are noted in the link section.
FORMULA
a(n) = ((4*n+7)*(4*n+2)) - (4*n+2) * (4*n+3)/2 + 4 for n > 2.
From Colin Barker, Jun 15 2018: (Start)
G.f.: x*(20 - 11*x + 12*x^2 - 5*x^3) / (1 - x)^3.
a(n) = -3 + 10*n + 8*n^2 for n>1.
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n > 4.
(End)
PROG
(PARI) concat(0, Vec(x*(20 - 11*x + 12*x^2 - 5*x^3) / (1 - x)^3 + O(x^50))) \\ Colin Barker, Jun 15 2018
CROSSREFS
Cf. A261347.
Sequence in context: A264444 A053245 A115882 * A277553 A260093 A304832
KEYWORD
nonn,easy
AUTHOR
Craig Knecht, Jun 15 2018
STATUS
approved