A309758 Numbers that are sums of consecutive powers of 3.

1, 3, 4, 9, 12, 13, 27, 36, 39, 40, 81, 108, 117, 120, 121, 243, 324, 351, 360, 363, 364, 729, 972, 1053, 1080, 1089, 1092, 1093, 2187, 2916, 3159, 3240, 3267, 3276, 3279, 3280, 6561, 8748, 9477, 9720, 9801, 9828, 9837, 9840, 9841, 19683, 26244, 28431

Offset

1,2

Comments

Numbers of the form (3^i - 3^j)/2 with i > j.

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

1080 = 3^3 + 3^4 + 3^5 + 3^6, so 1080 is in the sequence.
+------+--------+
| a(n) | base 3*|
+------+--------+
|   1  |     1  |
|   3  |    10  |
|   4  |    11  |
|   9  |   100  |
|  12  |   110  |
|  13  |   111  |
|  27  |  1000  |
|  36  |  1100  |
|  39  |  1110  |
|  40  |  1111  |
+------+--------+
* - a(n) written in base 3.

Maple

[seq(seq((3^i-3^j)/2, j=i-1..0, -1), i=1..20)]; # Robert Israel, Aug 19 2019

Crossrefs

Cf. A000244, A005836, A023758, A038464, A309759, A309761.

Sequence in context: A294229 A035256 A287400 * A047075 A104479 A067163

Adjacent sequences: A309755 A309756 A309757 * A309759 A309760 A309761

Keyword

nonn

Author

Ilya Gutkovskiy, Aug 15 2019

Status

approved