OFFSET
0,2
COMMENTS
Conjecture: the sequence is strictly increasing.
LINKS
Colin Barker, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (2,-1,2,-2).
FORMULA
G.f.: 1/(Sum_{k>=0} [(k+1)*r](-x)^k), where r = 8/5 and [ ] = floor.
From Colin Barker, Jul 14 2017: (Start)
G.f.: (1 + x)^2*(1 - x + x^2 - x^3 + x^4) / ((1 - x)*(1 - x - 2*x^3)).
a(n) = 2*a(n-1) - a(n-2) + 2*a(n-3) - 2*a(n-4) for n>3.
(End)
a(n) = abs(A279780(n)). - Alois P. Heinz, Jul 15 2017
MATHEMATICA
r = 8/5;
u = 1000; (* # initial terms from given series *)
v = 100; (* # coefficients in reciprocal series *)
CoefficientList[Series[1/Sum[Floor[r*(k + 1)] (-x)^k, {k, 0, u}], {x, 0, v}], x]
LinearRecurrence[{2, -1, 2, -2}, {1, 3, 5, 9, 17, 30, 52}, 40] (* Harvey P. Dale, Oct 13 2023 *)
PROG
(PARI) Vec((1 + x)^2*(1 - x + x^2 - x^3 + x^4) / ((1 - x)*(1 - x - 2*x^3)) + O(x^50)) \\ Colin Barker, Jul 20 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Jul 14 2017
STATUS
approved