EN|RU Volume 18, No 6, 2011, P. 33-60 UDC 519.174 E. V. Konstantinova, A. N. Medvedev Cycles of lentgth 9 in the pancake graph Abstract: A cycle $C_l$ of length $l$, where $6\le l\le n!$, can be embedded in the Pancake graph $P_n$, $n\ge3$, that is the Cayley graph on the symmetric group with the generating set of all prefix-reversals. The algebraic characterization of cycles of length six and seven via products of generating elements is known. We continue to study odd cycles. The explicit description of cycles of length nine by means of 10 canonical forms is given. It is also proved that each of vertices of $P_n$, $n\ge4,$ belongs to $\frac{8n^3-45n^2+61n-12}2$ cycles of length nine. In general, there are $O(n!\,n^3)$ different cycles of length nine in the graph. Ill. 5, tab. 1, bibliogr. 10. Keywords: admissible subgraph, indicator of subgraph’s quality, Pareto optimal subgraph. Konstantinova Elena Valentinovna 1,2 Medvedev Alexey Nikolaevich 2 1. S. L. Sobolev Institute of Mathematics, SB RAS, 4 Acad. Koptyug Ave., 630090 Novosibirsk, Russia 2. Novosibirsk State University, 2 Pirogov St., 630090 Novosibirsk, Russia e-mail: e_konsta@math.nsc.ru, an_medvedev@yahoo.com © Sobolev Institute of Mathematics, 2015