OFFSET
1,2
LINKS
R. Smith and V. Vatter, The enumeration of permutations sortable by pop stacks in parallel
FORMULA
G.f.: (1584*x^11-14016*x^10+45432*x^9-79454*x^8+86562*x^7-62624*x^6 +30887*x^5-10411* x^4+2352*x^3-339*x^2+28*x-1) / (7920*x^11-40116*x^10 +96324*x^9-139728*x^8+133468 *x^7-87278*x^6+39670*x^5-12495*x^4 +2666*x^3-366*x^2+29*x-1).
CROSSREFS
KEYWORD
nonn
AUTHOR
Vincent Vatter, Aug 29 2009
STATUS
approved