A318238 a(n) is the number of integer partitions of n for which the crank is equal to the index of the seaweed algebra formed by the integer partition paired with its weight.

0, 0, 1, 1, 1, 1, 2, 2, 2, 3, 6, 5, 5, 8, 14, 15, 15, 24, 27, 38, 47, 58, 66, 83, 92, 118, 156, 187, 234, 262, 329, 367, 446, 517, 657, 712, 890, 1041, 1270, 1411, 1751, 1951, 2350, 2678, 3278, 3715

Offset

1,7

Comments

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.

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.

a(n)>0 for n>2. To see this: if n=k+1 take the partition (k,1).

Links

Table of n, a(n) for n=1..46.

V. Coll, M. Hyatt, C. Magnant, H. Wang, Meander graphs and Frobenius seaweed Lie algebras II, Journal of Generalized Lie Theory and Applications 9 (1) (2015) 227.

V. Dergachev, A. Kirillov, Index of Lie algebras of seaweed type, J. Lie Theory 10 (2) (2000) 331-343.

Crossrefs

Cf. A237832, A318176, A318177, A318178, A318196, A318203

Sequence in context: A070610 A156820 A104346 * A341075 A193450 A109906

Adjacent sequences: A318235 A318236 A318237 * A318239 A318240 A318241

Keyword

nonn,more

Author

Nick Mayers, Melissa Mayers, Aug 21 2018

Status

approved