A336489 Consider the figure made up of a row of n adjacent congruent rectangles, with diagonals of all possible rectangles drawn; a(n) = number of interior vertices where exactly three lines cross.

0, 1, 2, 8, 18, 32, 50, 102, 126, 198, 286, 390, 510, 742, 878, 1130, 1414, 1770, 2166, 2778, 3186, 3858, 4594, 5342, 6146, 7342, 8294, 9662, 11134, 12710, 14390, 16582, 18226, 20518, 22946, 25662, 28530, 32270, 35250, 38862, 42650, 46614, 50754, 55990, 60730

Offset

1,3

Links

Lars Blomberg, Table of n, a(n) for n = 1..500

Formula

a(n) = A018810(n+1) / 2 for n > 2. - Andrei Zabolotskii, Jun 23 2026

Crossrefs

Cf. A334701, A336490, A336491, A018810.

Column 6 in A333275.

Sequence in context: A001105 A379803 A361905 * A051787 A050804 A081324

Adjacent sequences: A336486 A336487 A336488 * A336490 A336491 A336492

Keyword

nonn

Author

Lars Blomberg, Jul 25 2020

Status

approved