A324039 Row lengths of the irregular triangles A324038 and A324246.

1, 1, 2, 2, 4, 8, 11, 19, 31, 50, 88, 146, 241, 407, 675, 1118, 1871, 3102, 5175, 8633, 14394, 23999, 40002, 66666, 111044, 185192, 308442, 514138, 857283, 1428537, 2381021

Offset: 0

Author

Nicolas Vaillant, Philippe Delarue, Wolfdieter Lang, May 09 2019

Keywords

• nonn
• easy

Examples

			a(5) = 8 = 2*a(4) because a_1(4) =  A324040(4) = 0.
a(6) =  2*a(5) - 5 = 16 - 5 = 11  because a_1(5) = A324040(5) = 5.
		

Crossrefs

Cf. A324038, A324040, A324246.

Formula

a(n) = 2*a(n-1) - a_1(n-1), for n >= 2, and a(0) = 1 = a(1), where a_1(k) is the number of entries 1 (mod 3) in row k of A324246 given in A324040(k).