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A222637
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Squarefree part of the total number of arrangements of a set with n elements.
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4
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1, 2, 5, 1, 65, 326, 1957, 137, 109601, 986410, 9864101, 27126278, 7704505, 16926797486, 236975164805, 888656868019, 56874039553217, 966858672404690, 17403456103284421, 826664164906010, 6613313319248080001, 138879579704209680022, 3055350753492612960485
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OFFSET
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0,2
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LINKS
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FORMULA
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MAPLE
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add( n!/k!, k=0..n) ;
end proc:
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MATHEMATICA
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core[n_] := Times @@ Power @@@ ({#[[1]], Mod[#[[2]], 2]}& /@ FactorInteger[n]);
a[n_] := If[n == 0, 1, core[Floor[E*n!]]];
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PROG
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(PARI) a(n) = core(n! * polcoeff(exp(x + x*O(x^n)) / (1 - x), n))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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