A026041 a(n) = d(n)/2, where d = A026040.

12, 20, 32, 49, 72, 102, 140, 187, 244, 312, 392, 485, 592, 714, 852, 1007, 1180, 1372, 1584, 1817, 2072, 2350, 2652, 2979, 3332, 3712, 4120, 4557, 5024, 5522, 6052, 6615, 7212, 7844, 8512, 9217, 9960, 10742, 11564, 12427, 13332, 14280, 15272, 16309, 17392, 18522, 19700, 20927, 22204, 23532, 24912, 26345

Offset: 4

Author

Clark Kimberling

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 4..1000
• Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1).

Programs

Magma

[n*(n^2-3*n+14)/6: n in [4..60]]; // Vincenzo Librandi, Oct 17 2013

Mathematica

CoefficientList[Series[-(7 x^3 - 24 x^2 + 28 x - 12)/(x - 1)^4, {x, 0, 60}], x] (* Vincenzo Librandi, Oct 17 2013 *)

PARI

a(n)=n*(n^2-3*n+14)/6 \\ Charles R Greathouse IV, Oct 18 2022

Formula

For n>4, a(n) = a(n-1)+A022856(n+2). - Levi R. Self (levi.r.self(AT)gmail.com), Aug 04 2007

G.f.: -x^4*(7*x^3-24*x^2+28*x-12)/(x-1)^4. - Colin Barker, Oct 07 2012

a(n) = n*(n^2-3*n+14)/6. - Vincenzo Librandi, Oct 17 2013