cp's OEIS Frontend

A318203 a(n) is the number of integer partitions of n for which the largest part is equal to the index of the seaweed algebra formed by the integer partition paired with its weight.

%I A318203 #10 Sep 19 2018 06:17:59
%S A318203 0,0,1,1,0,1,1,3,3,3,5,6,6,10,13,18,18,27,31,40,52,58,78,95,103,136,
%T A318203 161,194,225,265,346,386,483,585,660,797,938,1134,1316,1521,1832,2081,
%U A318203 2550,2901,3407,3913,4614,5345,6305,7280,8514,9824,11377,13120,14960,17427,19981,23316,26859,30390
%N A318203 a(n) is the number of integer partitions of n for which the largest part is equal to the index of the seaweed algebra formed by the integer partition paired with its weight.
%C A318203 The index of a Lie algebra, g, is an invariant of the Lie algebra defined by min(dim(Ker(B_f)) where the min is taken over all linear functionals f on g and B_f denotes the bilinear form f([_,_]) were [,] denotes the bracket multiplication on g.
%C A318203 For seaweed subalgebras of sl(n), which are Lie subalgebras of sl(n) whose matrix representations are parametrized by an ordered pair of compositions of n, the index can be determined from a corresponding graph called a meander.
%C A318203 a(n) > 0 for n = 3, 4 and n > 5. To see this: for n odd if n=3 take the partition (1,1,1), if n > 5 take the partition (2,...,2,1,1,1,1,1); for n > 2 congruent to 2 (mod 6), say n=6k+2, take the partition (2k,1,...,1) with 4k+2 1's; for n > 0 congruent to 4 (mod 6), say n=6k+4, take the partition (2k+1, 1,...,1) with 4k+3 1's; for n > 0 congruent to 0 (mod 6), say n=6k, take the partition (2k, 2k, 2k-1, 1).
%H A318203 V. Coll, M. Hyatt, C. Magnant, H. Wang, <a href="http://dx.doi.org/10.4172/1736-4337.1000227">Meander graphs and Frobenius seaweed Lie algebras II</a>, Journal of Generalized Lie Theory and Applications 9 (1) (2015) 227.
%H A318203 V. Dergachev, A. Kirillov, <a href="https://www.emis.de/journals/JLT/vol.10_no.2/6.html">Index of Lie algebras of seaweed type</a>, J. Lie Theory 10 (2) (2000) 331-343.
%Y A318203 Cf. A237832, A318176, A318177, A318178, A318196
%K A318203 nonn
%O A318203 1,8
%A A318203 _Nick Mayers_, _Melissa Mayers_ Aug 21 2018