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%D J. Riordan, The enumeration of permutations with three-ply staircase restrictions, unpublished memorandum, Bell Telephone Laboratories, Murray Hill, NJ, Oct 1963.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 (unpublished memorandum, Bell Telephone Laboratories, Murray Hill, NJ, Oct 1963)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