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A346719
a(n) is the number of positive Euler permutations of order 2*n. Bisection (even indices) of A347601.
3
1, 0, 7, 102, 8109, 642220, 89458803, 15935870034, 3858227881945, 1176448390679256, 447692501190569823, 206713705368363820990, 114132862919751113790597, 74179275137980421348697732, 56081703047542413155379531979, 48790316146471264354636437276330, 48400301382766335524903922737193393
OFFSET
0,3
COMMENTS
For definitions and comments see A347601.
FORMULA
a(n) + A346720(n) = A000166(2n) (rencontres numbers).
a(n) - A346720(n) = A000364(n) (Euler secant numbers).
a(n) = subfactorial(2*n) / 2 + Im(PolyLog(-2*n, i)).
MAPLE
A346719 := n -> (A000166(2*n) + euler(2*n)) / 2:
seq(A346719(n), n = 0..16);
MATHEMATICA
A346719[n_] := Subfactorial[2 n]/2 + Im[PolyLog[-2 n, I]];
Table[A346719[n], {n, 0, 16}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Peter Luschny, Sep 09 2021
STATUS
approved