cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A106833 3n and 2n, alternating.

Original entry on oeis.org

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

Views

Author

Zak Seidov, May 19 2005

Keywords

Crossrefs

Cf. A118402 (first differences).

Programs

  • 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