A120159 a(n) = 15 + floor((2 + Sum_{j=1..n-1} a(j))/3).

15, 20, 27, 36, 48, 64, 85, 114, 152, 202, 270, 360, 480, 640, 853, 1137, 1516, 2022, 2696, 3594, 4792, 6390, 8520, 11360, 15146, 20195, 26927, 35902, 47870, 63826, 85102, 113469, 151292, 201723, 268964, 358618, 478158, 637544, 850058, 1133411

Offset: 1

Author

Graeme McRae, Jun 10 2006

Keywords

• nonn
• easy

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) >;
A120159:= func< n | g(n, 15, 2) >;
[A120159(n): n in [1..60]]; // G. C. Greubel, Aug 31 2023

Mathematica

A120159[n_]:= A120159[n]= 15 +Quotient[2 +Sum[A120159[k], {k,n-1}], 3];
Table[A120159[n], {n, 60}] (* G. C. Greubel, Aug 31 2023 *)

SageMath

@CachedFunction
def A120159(n): return 15 +(2+sum(A120159(k) for k in range(1, n)))//3
[A120159(n) for n in range(1, 61)] # G. C. Greubel, Aug 31 2023

Extensions

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