OFFSET
0,2
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..5000
Index entries for linear recurrences with constant coefficients, signature (3, -3, 1).
FORMULA
Conjectures from Colin Barker, Apr 07 2015: (Start)
a(n) = n*(3+n) = A028552(n) for n > 1.
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n > 4.
G.f.: x*(x^3 - 3*x^2 + 5*x - 5) / (x-1)^3. (End)
E.g.f.: x*(x+4)*exp(x) + x. - G. C. Greubel, Aug 28 2017
MAPLE
A033676 := proc(n) local a, d; a := 0 ; for d in numtheory[divisors](n) do if d^2 <= n then a := max(a, d) ; fi; od: a; end: A163280 := proc(n, k) local r, T ; r := 0 ; for T from k^2 by k do if A033676(T) = k then r := r+1 ; if r = n then RETURN(T) ; fi; fi; od: end: A164004 := proc(n) if n = 0 then 0; else A163280(4, n) ; fi; end: seq(A164004(n), n=0..80) ; # R. J. Mathar, Aug 09 2009
MATHEMATICA
Join[{0, 5}, Table[n*(n + 3), {n, 2, 50}]] (* G. C. Greubel, Aug 28 2017 *)
PROG
(PARI) x='x+O('x^50); concat([0], Vec(x*(x^3 -3*x^2 +5*x -5)/(x-1)^3)) \\ G. C. Greubel, Aug 28 2017
CROSSREFS
KEYWORD
nonn,easy,less
AUTHOR
Omar E. Pol, Aug 08 2009
EXTENSIONS
Extended beyond a(12) by R. J. Mathar, Aug 09 2009
STATUS
approved