a = 1.641, b = 1.902, c = 0.316, d= 1.525 a = 0.970, b = 1.899, c = 1.381,d = 1.506 a = 1.4, b = 2.3, c = 2.4, d = 2.1 a = 2.01, b = 2.53, c = 1.61, d = 0.33 a = 2.7, b = 0.09, c = 0.86, d = 2.2 a = 0.827, b = 1.637, c = 1.659, d = 0.943 a = 2.24, b = 0.43, c = 0.65, d = 2.43 a = 2, b = 2, c = 1.2, d = 2 a = 0.709, b = 1.638, c = 0.452, d = 1.740 Contribution by Johnny Svensson
A variation: y_{n+1} = c cos(a x_{n}) + cos(b y_{n})
The one ring a = 1.40, b = 1.56, c = 1.40, d = 6.56
