OFFSET
1,2
REFERENCES
H. L. Abbott and D. Hanson, A lattice path problem, Ars Combin., 6 (1978), 163-178.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
Michael De Vlieger, Table of n, a(n) for n = 1..1928
H. L. Abbott and D. Hanson, A lattice path problem, Ars Combin., 6 (1978), 163-178. (Annotated scanned copy)
Index entries for linear recurrences with constant coefficients, signature (4,-3,2,1).
FORMULA
a(n) = 1 + Sum_{k=1..n-1} A006189(k). - Sean A. Irvine, Jan 20 2017
From Colin Barker, Jan 20 2017: (Start)
a(n) = 4*a(n-1) - 3*a(n-2) + 2*a(n-3) + a(n-4) for n>4.
G.f.: x*(1 - 2*x) / ((1 - x + x^2)*(1 - 3*x - x^2)).
(End)
MATHEMATICA
LinearRecurrence[{4, -3, 2, 1}, {1, 2, 5, 16}, 30] (* Harvey P. Dale, Mar 22 2018 *)
CROSSREFS
KEYWORD
nonn,walk,easy
AUTHOR
EXTENSIONS
Offset corrected and more terms from Sean A. Irvine, Jan 20 2017
STATUS
approved