A120157 a(n) = 13 + floor(Sum_{j=1..n-1} a(j)/3).

13, 17, 23, 30, 40, 54, 72, 96, 128, 170, 227, 303, 404, 538, 718, 957, 1276, 1701, 2268, 3024, 4032, 5376, 7168, 9558, 12744, 16992, 22656, 30208, 40277, 53703, 71604, 95472, 127296, 169728, 226304, 301738, 402318, 536424, 715232, 953642

Offset: 1

Author

Graeme McRae, Jun 10 2006

Keywords

• nonn

Links

• Harvey P. Dale, 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) >;
A120157:= func< n | g(n, 13, 0) >;
[A120157(n): n in [1..60]]; // G. C. Greubel, Aug 31 2023

Mathematica

Module[{lst={13}},Do[AppendTo[lst,13+Floor[Total[lst]/3]],{40}];lst] (* Harvey P. Dale, May 22 2012 *)

SageMath

@CachedFunction
def A120157(n): return 13 +(sum(A120157(k) for k in range(1, n)))//3
[A120157(n) for n in range(1, 61)] # G. C. Greubel, Aug 31 2023

Extensions

Name edited by G. C. Greubel, Aug 31 2023