OFFSET
0,2
LINKS
Index entries for linear recurrences with constant coefficients, signature (7, -8, -6, 6).
FORMULA
For n>4, a(n) = 7*a(n-1) - 8*a(n-2) - 6*a(n-3) + 6*a(n-4), a(1)=7, a(2)=37, a(3)=197, a(4)=1049.
G.f.: (1-4*x^2+2*x^4)/(1-7*x+8*x^2+6*x^3-6*x^4).
EXAMPLE
For n=2 the a(2)=37=49-12 sequences contain every combination except these twelve: 01,10,12,21,23,32,34,43,45,54,56,65.
MATHEMATICA
LinearRecurrence[{7, -8, -6, 6}, {1, 7, 37, 197, 1049}, 40]
PROG
(Python)
def a(n):
.if n in [0, 1, 2, 3, 4]:
..return [1, 7, 37, 197, 1049][n]
.return 7*a(n-1)-8*a(n-2)-6*a(n-3)+6*a(n-4)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
David Nacin, Jun 01 2017
STATUS
approved