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A001888
Hit polynomials.
(Formerly M3573 N1449)
1
1, 1, 1, 4, 21, 122, 849, 6719, 59873, 593686, 6483027, 77309508, 999569969, 13927664613, 208044077633, 3316415176712, 56193522437465, 1008499234742158, 19110533105114433, 381290148293261075, 7989548583615385153, 175418232627066361514, 4027213499971769192903, 96489861550805864197512
OFFSET
1,4
REFERENCES
J. Riordan, The enumeration of permutations with three-ply staircase restrictions, unpublished memorandum, Bell Telephone Laboratories, Murray Hill, NJ, Oct 1963. (See A001883)
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
N. J. A. Sloane, Annotated copy of Riordan's Three-Ply Staircase paper (unpublished memorandum, Bell Telephone Laboratories, Murray Hill, NJ, Oct 1963)
CROSSREFS
Second column of A080061.
Sequence in context: A274969 A236525 A277292 * A103769 A003014 A108404
KEYWORD
nonn
EXTENSIONS
More terms from Vladeta Jovovic, Vladimir Baltic, Jan 23 2003
a(21)-a(24) from Vaclav Kotesovec, Oct 10 2017
STATUS
approved