A106833 3n and 2n, alternating.
3, 4, 9, 8, 15, 12, 21, 16, 27, 20, 33, 24, 39, 28, 45, 32, 51, 36, 57, 40, 63, 44, 69, 48, 75, 52, 81, 56, 87, 60, 93, 64, 99, 68, 105, 72, 111, 76, 117, 80, 123, 84, 129, 88, 135, 92, 141, 96, 147, 100, 153, 104, 159, 108, 165, 112, 171, 116, 177, 120, 183
Offset: 1
Links
- Index entries for linear recurrences with constant coefficients, signature (0,2,0,-1).
Crossrefs
Cf. A118402 (first differences).
Programs
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Mathematica
Table[n(2 + Mod[n, 2]), {n, 50}] -
PARI
a(n)=sumdiv(n,d,moebius(d)*sigma(2*n/d)) \\ Benoit Cloitre, Oct 18 2009
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
Extensions
More terms from Michel Marcus, May 17 2014