A049933 a(n) = a(1) + a(2) + ... + a(n-1) + a(m) for n >= 4, where m = 2^(p+1) + 2 - n and p is the unique integer such that 2^p < n - 1 <= 2^(p+1), starting with a(1) = a(2) = a(3) = 1.

1, 1, 1, 4, 8, 19, 35, 70, 140, 349, 663, 1310, 2609, 5214, 10425, 20850, 41700, 104249, 198073, 390935, 779265, 1557231, 3113815, 6227316, 12454423, 24908776, 49817517, 99635018, 199270025, 398540046, 797080089, 1594160178, 3188320356, 7970800889, 15144521689

Offset: 1

Author

Clark Kimberling

Keywords

• nonn

Examples

			From _Petros Hadjicostas_, Nov 06 2019: (Start)
a(4) = a(2^ceiling(log_2(4-1)) + 2 - 4) + a(1) + a(2) + a(3) = a(2) + a(1) + a(2) + a(3) = 4.
a(5) = a(2^ceiling(log_2(5-1)) + 2 - 5) + a(1) + a(2) + a(3) + a(4) = a(1) + a(1) + a(2) + a(3) + a(4) = 8.
a(6) = a(2^ceiling(log_2(6-1)) + 2 - 6) + a(1) + a(2) + a(3) + a(4) + a(5) = a(4) + a(1) + a(2) + a(3) + a(4) + a(5) = 19.
a(7) =  a(7 - 1 - A006257(7-2)) + Sum_{i = 1..6} a(i) = a(3) +  Sum_{i = 1..6} a(i) = 35.
a(8) =  a(8 - 1 - A006257(8-2)) + Sum_{i = 1..7} a(i) = a(2) +  Sum_{i = 1..7} a(i) = 70. (End)
		

Crossrefs

Cf. A006257, A049885 (similar, but with minus a(m)), A049937, A049945.

Programs

Maple

s := proc(n) option remember; `if`(n < 1, 0, a(n) + s(n - 1)); end proc;
a := proc(n) option remember;
  `if`(n < 4, 1, s(n - 1) + a(Bits:-Iff(n - 2, n - 2) + 3 - n));
end proc;
seq(a(n), n = 1 .. 30);

Mathematica

b[n_] := Module[{p}, For[p = 0, True, p++, If[2^p < n - 1 <= 2^(p + 1), Return[p]]]];
a[n_] := a[n] = If[n < 4, 1, With[{m = 2^(b[n] + 1) + 2 - n}, Total[ Array[a, n - 1]] + a[m]]];
Array[a, 35] (* Jean-François Alcover, Apr 24 2020 *)

Formula

From Petros Hadjicostas, Nov 06 2019: (Start)

a(n) = a(2^ceiling(log_2(n-1)) + 2 - n) + Sum_{i = 1..n-1} a(i) for n >= 4.

a(n) = a(n - 1 - A006257(n-2)) + Sum_{i = 1..n-1} a(i) for n >= 4. (End)

Extensions

Name edited by and more terms from Petros Hadjicostas, Nov 06 2019