OFFSET
1,2
LINKS
Index entries for linear recurrences with constant coefficients, signature (1,2,-2,-1,1).
FORMULA
From Chai Wah Wu, Jun 09 2020: (Start)
a(n) = a(n-1) + 2*a(n-2) - 2*a(n-3) - a(n-4) + a(n-5) for n > 6.
G.f.: x*(x^5 - x^4 - x - 1)/((x - 1)^3*(x + 1)^2). (End)
From Bernard Schott, Jun 10 2020: (Start)
Bisections are:
a(1) = 1 and a(2k+1) = A028552(k) for k >= 1,
a(2k) = A002378(k) for k >= 1, hence,
a(2k+2) = a(2k+1) + 2 for k >= 1. (End)
MATHEMATICA
a[n_] := If[n == 1, 1, If[Mod[n, 2] == 0, n^2/4 + n/2, n^2/4 + n - 5/4]];
Table[a[n], {n, 1, 100}]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Roger L. Bagula, Dec 15 2008
STATUS
approved