A287812 Number of octonary sequences of length n such that no two consecutive terms have distance 1.

1, 8, 50, 314, 1972, 12386, 77796, 488636, 3069120, 19277130, 121079578, 760500364, 4776699874, 30002433636, 188445170924, 1183623397912, 7434334035874, 46695023649050, 293291264969380, 1842161313673506, 11570608166423524, 72674945645197500

Offset: 0

Author

David Nacin, Jun 02 2017

Keywords

• nonn
• easy

Examples

			For n=2 the a(2) = 64 - 14 = 50 sequences contain every combination except these fourteen: 01,10,12,21,23,32,34,43,45,54,56,65,67,76.
		

Links

• Index entries for linear recurrences with constant coefficients, signature (7, -3, -10, 3).

Crossrefs

Cf. A040000, A003945, A083318, A078057, A003946, A126358, A003946, A055099, A003947, A015448, A126473. A287804-A287819.

Programs

Mathematica

LinearRecurrence[{7, -3, -10, 3}, {1, 8, 50, 314, 1972}, 40]

Python

def a(n):
 if n in [0, 1, 2, 3, 4]:
  return [1, 8, 50, 314, 1972][n]
 return 7*a(n-1)-3*a(n-2)-10*a(n-3)+3*a(n-4)

Formula

For n>4, a(n) = 7*a(n-1) - 3*a(n-2) - 10*a(n-3) + 3*a(n-2), a(0)=1, a(1)=8, a(2)=50, a(3)=314, a(4)=1972.

G.f.: (-1 - x + 3 x^2 + 2 x^3 - x^4)/(-1 + 7 x - 3 x^2 - 10 x^3 + 3 x^4).