OFFSET
1,3
LINKS
Dean Hickerson, Counting Horizontally Convex Polyominoes, J. Integer Sequences, Vol. 2 (1999), #99.1.8.
Index entries for linear recurrences with constant coefficients, signature (5, -7, 4).
FORMULA
MATHEMATICA
a[ n_ ] := a[ n ]=If[ n<5, {1, 1, 3, 10}[ [ n ] ], 5a[ n-1 ]-7a[ n-2 ]+4a[ n-3 ] ]
LinearRecurrence[{5, -7, 4}, {1, 1, 3, 10, 33, 107}, 40] (* Harvey P. Dale, Nov 19 2019 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Dean Hickerson, Aug 10 1999
STATUS
approved