A296421 - OEIS

%I #17 Dec 18 2017 16:03:46

%S 1,2,3,4,4,6,6,8,7,9,9,10,11,11,12,12,14,16,13,16,16,19,16,20,17,22,

%T 19,22,21,24,22,26,22,28,24,29,26,28,29,30,30,31,32,32,33,33,34,35,35,

%U 36,36,38,40,39,38,42,41,42,44,41,43,45,51,40,44,53,46,51,44,55,47,53,54,51,55

%N a(1) = 1, a(2) = 2, a(3) = 3, a(4) = a(5) = 4, a(6) = a(7) = 6; a(n) = a(n-a(n-1)) + a(n-a(n-2)) + a(n-a(n-3)) for n > 7.

%H Altug Alkan, <a href="/A296421/b296421.txt">Table of n, a(n) for n = 1..10000</a>

%H Altug Alkan, <a href="/A296421/a296421.png">Alternative scatterplot of A296421</a>

%H Altug Alkan, <a href="/A296421/a296421_1.png">Scatterplot of a(n) - 2*n/3</a>

%t Fold[Append[#1, #1[[#2 - #1[[#2 - 1]] ]] + #1[[#2 - #1[[#2 - 2]] ]] + #1[[#2 - #1[[#2 - 3]] ]] ] &, {1, 2, 3, 4, 4, 6, 6}, Range[8, 75]] (* _Michael De Vlieger_, Dec 12 2017 *)

%o (PARI) q=vector(10^5); q[1]=1;q[2]=2;q[3]=3;q[4]=4;q[5]=4;q[6]=6;q[7]=6;for(n=8, #q, q[n] = q[n-q[n-1]]+q[n-q[n-2]]+q[n-q[n-3]]); q

%Y Cf. A005185, A284644, A278055, A292351.

%K nonn,look

%O 1,2

%A _Altug Alkan_, Dec 12 2017