OFFSET
1,1
LINKS
Index entries for linear recurrences with constant coefficients, signature (0,2,0,-1).
FORMULA
a(n) = n*(2 + (n mod 2)).
a(2*n) = 6*n + 3 = A016945(n). - Paul Curtz, Nov 23 2008
a(2*n+1) = A008586(n+1).
From R. J. Mathar, Apr 08 2009: (Start)
G.f.: x*(3+4*x+3*x^2)/((x-1)^2*(1+x)^2).
a(n) = 2*a(n-2) - a(n-4). (End)
a(n) = Sum_{d|n} mu(d)*sigma(2*n/d). - Benoit Cloitre, Oct 18 2009
a(n) = n*(5-(-1)^n)/2. - Wesley Ivan Hurt, May 14 2014
MATHEMATICA
Table[n(2 + Mod[n, 2]), {n, 50}]
PROG
(PARI) a(n)=sumdiv(n, d, moebius(d)*sigma(2*n/d)) \\ Benoit Cloitre, Oct 18 2009
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Zak Seidov, May 19 2005
EXTENSIONS
More terms from Michel Marcus, May 17 2014
STATUS
approved