A001728 Expansion of cos x / cos 4x.

1, 15, 1185, 230895, 83860545, 48942778575, 41893214676705, 49441928730798255, 76946148390480577665, 152682246738275154625935, 376229085883258481118811425, 1127131459348047116845576437615, 4034538627668651235506091915425985

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn

Links

• T. D. Noe, Table of n, a(n) for n = 0..50

Crossrefs

Bisection of A000813.

Programs

Mathematica

nn = 22; t = Range[0, nn]! CoefficientList[Series[Cos[x]/Cos[4 x], {x, 0, nn}], x]; Take[t, {1, nn, 2}];