OFFSET
1,1
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..250
Index entries for linear recurrences with constant coefficients, signature (1,322,-322,-1,1).
FORMULA
The subsequences with odd indices and even indices satisfy the same recurrence relations: a(n+2) = 322*a(n+1) - a(n) - 680 and a(n+1) = 161*a(n) - 340 + 9*sqrt(320*a(n)^2 - 1360*a(n) - 175).
G.f.: -5*x*(11+486*x-635*x^2+2*x^4) / ( (x-1)*(x^2+18*x+1)*(x^2-18*x+1) ).
EXAMPLE
a(1) = 55 = 3+6+10+15+21.
MAPLE
a:= n-> `if`(n<2, [0, 55][n+1], (<<0|1|0>, <0|0|1>, <1|-323|323>>^iquo(n-2, 2, 'r'). `if`(r=0, <<2485, 799480, 257429395>>, <<17020, 5479705, 1764447310>>))[1, 1]): seq(a(n), n=1..20); # Alois P. Heinz, Sep 25 2008, revised Dec 15 2011
MATHEMATICA
LinearRecurrence[{1, 322, -322, -1, 1}, {55, 2485, 17020, 799480, 5479705}, 20] (* Jean-François Alcover, Oct 05 2019 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Richard Choulet, Oct 06 2007
EXTENSIONS
More terms from Alois P. Heinz, Sep 25 2008
a(6) and a(8) corrected by Harvey P. Dale, Oct 02 2011
a(10), a(12), a(14) corrected at the suggestion of Harvey P. Dale by D. S. McNeil, Oct 02 2011
STATUS
approved