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A309758
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Numbers that are sums of consecutive powers of 3.
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4
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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
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OFFSET
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1,2
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COMMENTS
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Numbers of the form (3^i - 3^j)/2 with i > j.
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LINKS
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EXAMPLE
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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.
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MAPLE
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[seq(seq((3^i-3^j)/2, j=i-1..0, -1), i=1..20)]; # Robert Israel, Aug 19 2019
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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