A243572 - OEIS

A243572

Irregular triangular array generated as in Comments; contains every positive integer exactly once.

1, 2, 3, 4, 6, 9, 5, 7, 10, 12, 18, 27, 8, 11, 13, 15, 19, 21, 28, 30, 36, 54, 81, 14, 16, 20, 22, 24, 29, 31, 33, 37, 39, 45, 55, 57, 63, 82, 84, 90, 108, 162, 243, 17, 23, 25, 32, 34, 38, 40, 42, 46, 48, 56, 58, 60, 64, 66, 72, 83, 85, 87, 91, 93, 99, 109

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OFFSET

1,2

COMMENTS

Decree that row 1 is (1), row 2 is (2, 3), and row 3 is (4, 6, 9). Let r(n) = A001590(n+2), so that r(r) = r(n-1) + r(n-2) + r(n-3) with r(1) =1, r(2) = 2, r(3) = 3. Row n of the array, for n >= 4, consists of the numbers, in increasing order, defined as follows: all 3*x from x in row n-1, together with all 1 + 3*x from x in row n-2, together with all 2 + 3*x from x in row n-3. Thus, the number of numbers in row n is r(n), a tribonacci number. Every positive integer occurs exactly once in the array, so that the resulting sequence is a permutation of the positive integers.

LINKS

Clark Kimberling, Table of n, a(n) for n = 1..1500

EXAMPLE

First 5 rows of the array:

2 ... 3

4 ... 6 ... 9

5 ... 7 ... 10 .. 12 .. 18 .. 27

8 ... 11 .. 13 .. 15 .. 19 .. 21 .. 28 .. 30 .. 36 .. 54 .. 81

MATHEMATICA

z = 10; g[1] = {1}; f1[x_] := x + 1; f2[x_] := 3 x; h[1] = g[1];

b[n_] := b[n] = DeleteDuplicates[Union[f1[g[n - 1]], f2[g[n - 1]]]];

h[n_] := h[n] = Union[h[n - 1], g[n - 1]];