OFFSET
0,3
COMMENTS
Arises from counting of symmetric tensor invariants without color. See Geloun-Ramgoolam, Section 6.2 for information and Mathematica code.
LINKS
Mehmet Emin Aktas, Dessins d'Enfants of Trigonal Curves, arXiv:1706.09956 [math.AG], 2017, Theorem 5.
J. B. Geloun, S. Ramgoolam, Counting Tensor Model Observables and Branched Covers of the 2-Sphere, arXiv preprint arXiv:1307.6490 [hep-th], 2013.
Brendan McKay, Number of all different n-by-n matrices where sum of rows and columns is 3, MathOverflow, 2016.
B. D. McKay and N. C. Wormald, Autormorphisms of Random Graphs with Specified Vertices. Combinatorica 4 (4) (1984) 325-338.
FORMULA
a(n) = 1 + Sum_{i=1..n} A328159(i). - Brendan McKay, Oct 05 2019
EXAMPLE
a(2) = 2 because there are 2 such 2 X 2 matrices: [1 2;2 1] and [3 0;0 3]. - Nathaniel Johnston, Oct 12 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Nov 22 2013
EXTENSIONS
New name and a(9)-a(11) from Nathaniel Johnston, Oct 12 2016
a(12) and a(13) from Brendan McKay, Oct 05 2019
a(0)=1 prepended, a(12)-a(13) corrected and terms a(14) and beyond from Andrew Howroyd, Apr 04 2020
STATUS
approved