%I #17 Oct 28 2024 15:09:04
%S 2,126,49410,48649086,89434106370,264235243691646,1145011717430672130,
%T 6841110155700330881406,53899295662946509072626690,
%U 541439307193573593050370186366,6754273504043546592593642328610050,102439130403410639137159601119206854526
%N Generalized Euler number c(9,n).
%H Matthew House, <a href="/A064070/b064070.txt">Table of n, a(n) for n = 0..174</a>
%H D. Shanks, <a href="http://dx.doi.org/10.1090/S0025-5718-1967-0223295-5">Generalized Euler and class numbers</a>. Math. Comp. 21 (1967) 689-694.
%H D. Shanks, <a href="http://dx.doi.org/10.1090/S0025-5718-1968-0227093-9">Corrigenda to: "Generalized Euler and class numbers"</a>, Math. Comp. 22 (1968), 699.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/EulerNumber.html">Euler Number</a>.
%F a(n) = (2*n)!*[x^(2*n)](sec(9*x)*2*cos(3*x)^2). - _Peter Luschny_, Nov 21 2021
%p egf := sec(9*x)*2*cos(3*x)^2: ser := series(egf, x, 24):
%p seq((2*n)!*coeff(ser, x, 2*n), n = 0..10); # _Peter Luschny_, Nov 21 2021
%t Range[0, 22, 2]! CoefficientList[Series[2 Sec[9 x] Cos[3 x]^2, {x, 0, 22}], x^2] (* _Matthew House_, Oct 27 2024 *)
%Y Row 9 of A235605.
%Y Cf. A064074, A349268, A349264.
%K nonn,easy,changed
%O 0,1
%A _Eric W. Weisstein_, Aug 31 2001