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A026520 a(n) = T(n,n), T given by A026519. Also a(n) = number of integer strings s(0),...,s(n), counted by T, such that s(n)=0. 8
1, 1, 2, 4, 8, 20, 38, 104, 196, 556, 1052, 3032, 5774, 16778, 32146, 93872, 180772, 529684, 1024256, 3008864, 5837908, 17184188, 33433996, 98577712, 192239854, 567591142, 1109049320, 3278348608, 6416509142, 18986482250 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..29.

Veronika Irvine, Lace Tessellations: A mathematical model for bobbin lace and an exhaustive combinatorial search for patterns, PhD Dissertation, University of Victoria, 2016.

Veronika Irvine, Stephen Melczer, Frank Ruskey, Vertically constrained Motzkin-like paths inspired by bobbin lace, arXiv:1804.08725 [math.CO], 2018.

FORMULA

For n>1, a(n) = 2*A026554(n-1).

CROSSREFS

Cf. A026519, A026521, A026522, A026523, A026524.

Sequence in context: A222562 A252891 A102634 * A282983 A282953 A283047

Adjacent sequences:  A026517 A026518 A026519 * A026521 A026522 A026523

KEYWORD

nonn

AUTHOR

Clark Kimberling

STATUS

approved

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Last modified November 17 23:26 EST 2019. Contains 329242 sequences. (Running on oeis4.)