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A164872
The number of permutations of length n that can be sorted by 4 pop stacks in parallel.
0
1, 2, 6, 24, 120, 718, 4884, 35546, 264590, 1969912, 14560996, 106781758, 778073440, 5643649364, 40811356112, 294554236798, 2123419108962, 15296729408614, 110149122090326, 792974948890068, 5707931771206042
OFFSET
1,2
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
Sequence in context: A177524 A223905 A374620 * A226437 A224287 A248838
KEYWORD
nonn
AUTHOR
Vincent Vatter, Aug 29 2009
STATUS
approved