OFFSET
0,2
COMMENTS
A diagonal of the square array A217770.
LINKS
Index entries for linear recurrences with constant coefficients, signature (8, -21, 20, -5).
FORMULA
a(n) = A217770(n,n+2).
a(n) = 8*a(n-1) - 21*a(n-2) + 20*a(n-3) - 5*a(n-4) for n>=4, a(0) = 1, a(1) = 4, a(2) = 15, a(3) = 56.
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Philippe Deléham, Mar 24 2013
STATUS
approved