OFFSET
1,2
COMMENTS
Also, the number of signed permutations w in the hyperoctahedral group whose initial interval [id,w] in Bruhat order is rank symmetric. Equivalently, the Kazhdan-Lusztig polynomial P_id,w(q) = 1. Characterized by pattern avoidance.
REFERENCES
S. Billey, Pattern avoidance and rational smoothness of Schubert varieties, Advances in Math, vol. 139 (1998) pp. 141-156.
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Sara Billey, Apr 01 2013
STATUS
approved