A242290 Positive integers k for which the k-th tetrahedral number is greedy-summable.

5, 6, 8, 9, 10, 11, 14, 15, 19, 20, 21, 23, 24, 25, 27, 29, 30, 33, 34, 35, 38, 40, 41, 43, 44, 45, 47, 48, 49, 50, 51, 54, 55, 56, 59, 61, 63, 64, 65, 67, 68, 69, 70, 71, 74, 75, 76, 78, 79, 81, 83, 85, 90, 93, 98, 99, 104, 105, 106, 107, 108, 109, 110, 114

Offset

1,1

Comments

Greedy summability is defined at A242288.

Links

Clark Kimberling, Table of n, a(n) for n = 1..1000

Example

Let s(n) = n(n+1)(n+2)/6 = A000292(n).  Then
a(1) = 5; s(5) = 35 = 20 + 10 + 4 + 1;
a(2) = 6; s(6) = 56 = 35 + 20 + 1;
a(3) = 8; s(8) = 120 = 84 + 35 + 1;
a(4) = 9; s(9) = 165 = 120 + 35 + 10.

Mathematica

z = 200;  s = Table[n (n + 1)(n + 2)/6, {n, 1, z}]; t = Table[{s[[n]], #, Total[#] == s[[n]]} &[DeleteCases[-Differences[FoldList[If[#1 - #2 >= 0, #1 - #2, #1] &, s[[n]], Reverse[Select[s, # < s[[n]] &]]]], 0]], {n, z}]
r[n_] := s[[n]] - Total[t[[n]][[2]]];
tr = Table[r[n], {n, 2, z}]  (* A242288 *)
c = Table[Length[t[[n]][[2]]], {n, 2, z}] (* A242289 *)
f = 1 + Flatten[Position[tr, 0]]  (* A242290 *)
f (f + 1)(f + 2)/6  (* A242291 *) (* Peter J. C. Moses, May 06 2014 *)

Crossrefs

Cf. A242288, A242289, A242291, A241833, A242284, A000292.

Sequence in context: A270653 A299538 A201512 * A296562 A057854 A033266

Adjacent sequences: A242287 A242288 A242289 * A242291 A242292 A242293

Keyword

nonn,easy

Author

Clark Kimberling, May 10 2014

Status

approved