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A331449
a(0) = 1 by convention; for n>0, a(n) is the number of points in the n-th figure shown in A255011 (meaning the figure with 4n points on the perimeter).
13
1, 5, 37, 257, 817, 2757, 4825, 12293, 19241, 33549, 49577, 87685, 101981, 178465, 220113, 286357, 379097, 551669, 606241, 880293, 951445, 1209049, 1507521, 1947877, 2002669, 2624409, 3056093, 3550425, 3955049, 5069037, 5062153, 6669665, 7081969, 8143193, 9365089, 10296469
OFFSET
0,2
COMMENTS
Equivalently, this is A334690(n) + 4*n.
LINKS
Lars Blomberg, Scott R. Shannon, and N. J. A. Sloane, Graphical Enumeration and Stained Glass Windows, 1: Rectangular Grids, (2021). Also arXiv:2009.07918.
N. J. A. Sloane, "A Handbook of Integer Sequences" Fifty Years Later, arXiv:2301.03149 [math.NT], 2023, p. 20.
Scott R. Shannon, Image for n = 1.
Scott R. Shannon, Image for n = 2.
Scott R. Shannon, Image for n = 3.
Scott R. Shannon, Image for n = 4.
Scott R. Shannon, Image for n = 5.
Scott R. Shannon, Image for n = 10.
FORMULA
By Euler's formula, a(n) = A331448(n) - A255011(n) + 1.
CROSSREFS
For the circular analog see A006533, A007678, A007569, A135565.
Sequence in context: A080507 A108049 A121141 * A220634 A083232 A236581
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jan 23 2020
EXTENSIONS
a(11)-a(35) from Giovanni Resta, Jan 28 2020
STATUS
approved