A000192 Generalized Euler numbers c(6,n).

2, 46, 7970, 3487246, 2849229890, 3741386059246, 7205584123783010, 19133892392367261646, 67000387673723462963330, 299131045427247559446422446, 1658470810032820740402966226850, 11179247066648898992009055586869646, 90035623994788132387893239340761189570

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• easy

References

• 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

• Sean A. Irvine, Table of n, a(n) for n = 0..250
• D. Shanks, Generalized Euler and class numbers, Math. Comp. 21 (1967) 689-694.
• D. Shanks, Corrigenda to: "Generalized Euler and class numbers", Math. Comp. 22 (1968), 699.
• D. Shanks, Generalized Euler and class numbers, Math. Comp. 21 (1967), 689-694; 22 (1968), 699. [Annotated scanned copy]
• Eric Weisstein's World of Mathematics, Euler Number.

Crossrefs

Row 6 of A235605.

Cf. A000187, A000191, A000411, A001587, A349264.

Programs

Maple

egf := sec(6*x)*(cos(x) + cos(5*x)): ser := series(egf, x, 24):
seq((2*n)!*coeff(ser, x, 2*n), n = 0..10); # Peter Luschny, Nov 21 2021

Mathematica

L[ a_, s_, t_:10000 ] := Plus@@Table[ N[ JacobiSymbol[ -a, 2k+1 ](2k+1)^(-s), 30 ], {k, 0, t} ]; c[ a_, n_, t_:10000 ] := (2n)!/Sqrt[ a ](2a/Pi)^(2n+1)L[ a, 2n+1, t ] (* Eric W. Weisstein, Aug 30 2001 *)

Sage

t = PowerSeriesRing(QQ, 't', default_prec=24).gen()
f = 2 * cos(3 * t) / (2 * cos(4 * t) - 1)
f.egf_to_ogf().list()[::2] # F. Chapoton, Oct 06 2020

Formula

E.g.f.: 2*cos(3*x) / (2*cos(4*x) - 1). - F. Chapoton, Oct 06 2020

a(n) = (2*n)!*[x^(2*n)](sec(6*x)*(cos(x) + cos(5*x))). - Peter Luschny, Nov 21 2021

a(n) ~ 2^(6*n + 5/2) * 3^(2*n + 1/2) * n^(2*n + 1/2) / (Pi^(2*n + 1/2) * exp(2*n)). - Vaclav Kotesovec, Apr 15 2022

Extensions

More terms from Eric W. Weisstein, Aug 30 2001