A120156 a(n) = 11 + floor((2 + Sum_{j=1..n-1} a(j))/3).

11, 15, 20, 27, 36, 48, 64, 85, 113, 151, 201, 268, 358, 477, 636, 848, 1131, 1508, 2010, 2680, 3574, 4765, 6353, 8471, 11295, 15060, 20080, 26773, 35697, 47596, 63462, 84616, 112821, 150428, 200571, 267428, 356570, 475427, 633903, 845204

Offset: 1

Author

Graeme McRae, Jun 10 2006

Keywords

• nonn

Links

• G. C. Greubel, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A072493, A073941, A112088.

Programs

Magma

function f(n, a, b)
  t:=0;
    for k in [1..n-1] do
      t+:= a+Floor((b+t)/3);
    end for;
  return t;
end function;
g:= func< n, a, b | f(n+1, a, b)-f(n, a, b) >;
A120156:= func< n | g(n, 11, 2) >;
[A120156(n): n in [1..60]]; // G. C. Greubel, Jul 06 2023

Mathematica

A120156[n_]:= A120156[n]= 11 +Quotient[2+Sum[A120156[k], {k,n-1}], 3];
Table[A120156[n], {n,60}] (* G. C. Greubel, Jul 06 2023 *)

SageMath

@CachedFunction
def A120156(n): return 11 +(2+sum(A120156(k) for k in range(1, n)))//3
[A120156(n) for n in range(1, 61)] # G. C. Greubel, Jul 06 2023