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Hit polynomials.
(Formerly M3345 N1346)
1

%I M3345 N1346 #24 Dec 23 2021 22:44:30

%S 1,4,8,38,209,1400,10849,95516,938441,10179149,120748974,1554688240,

%T 21588485677,321561688748,5113709884902,86469576394028,

%U 1549114961438599,29309613834899864,583986501706555597,12222118836543561940,268060239251978779839,6148136982942476816891

%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%D J. Riordan, The enumeration of permutations with three-ply staircase restrictions, unpublished memorandum, Bell Telephone Laboratories, Murray Hill, NJ, Oct 1963.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 (unpublished memorandum, Bell Telephone Laboratories, Murray Hill, NJ, Oct 1963)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 Third column of A080061.

%Y Cf. A001883-A001891.

%K nonn

%O 2,2

%A _N. J. A. Sloane_

%E More terms from _Vladeta Jovovic_, _Vladimir Baltic_, Jan 23 2003

%E a(21)-a(23) from _Vaclav Kotesovec_, Oct 10 2017