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Hit polynomials.
(Formerly M2117 N0835)
2

%I M2117 N0835 #26 Dec 23 2021 22:47:54

%S 1,0,1,2,20,104,775,6140,55427,553802,6087992,72994152,948103477,

%T 13262133736,198769630061,3177862894922,53984653965996,

%U 971068821144112,18438722595913195,368558842844143268,7735520783692157215,170095060428041137778,3910332719957508452016,93806427360751009531632

%N Hit polynomials.

%D J. Riordan, The enumeration of permutations with three-ply staircase restrictions, unpublished memorandum, Bell Telephone Laboratories, Murray Hill, NJ, Oct 1963. See A001883.

%D N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

%H N. J. A. Sloane, <a href="/A001883/a001883_21.pdf">Annotated copy of Riordan's Three-Ply Staircase paper</a> (unpublished memorandum, Bell Telephone Laboratories, Murray Hill, NJ, Oct 1963)

%Y Second column of A080018.

%Y Cf. A001883-A001891.

%K nonn

%O 1,4

%A _N. J. A. Sloane_

%E More terms from _Vladeta Jovovic_ and _Vladimir Baltic_, Jan 20 2003

%E a(21)-a(24) from _Vaclav Kotesovec_, Oct 10 2017