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URL: https://oeis.org/A326328

⇱ A326328 - OEIS

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A326328
a(n) = (2*n)! [x^(2*n)] cosh(x)^(-3).
1
1, -3, 33, -723, 25953, -1376643, 101031873, -9795436563, 1212135593793, -186388033956483, 34859622790687713, -7791941518975112403, 2051293521728340489633, -628173356956461494680323, 221398076445213367209575553, -88980467736394156270609236243, 40450409313733718675802456121473
OFFSET
0,2
COMMENTS
Apparently all terms except the initial 1 have 3-valuation 1. - F. Chapoton, Nov 25 2021
REFERENCES
H. S. Wall, Analytic Theory of Continued Fractions, Chelsea 1973, p. 206.
FORMULA
O.g.f. as a Stieltjes-type continued fraction: 1/(1 + 3*x/(1 + 8*x/(1 + 15*x/(1 +... + n*(n + 2)*x/(1 + ... ))))). See Wall, Chapter XI, eqn. 53.11 with k = 3. - Peter Bala, Dec 13 2025
MAPLE
egf := cosh(z)^(-3): ser := series(egf, z, 36):
seq((2*n)!*coeff(ser, z, 2*n), n=0..16);
CROSSREFS
Row 3 of A326327.
Sequence in context: A380722 A091462 A340971 * A233319 A003715 A247030
KEYWORD
sign,easy
AUTHOR
Peter Luschny, Jul 07 2019
STATUS
approved