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A025631
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Numbers of form 7^i*9^j, with i, j >= 0.
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3
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1, 7, 9, 49, 63, 81, 343, 441, 567, 729, 2401, 3087, 3969, 5103, 6561, 16807, 21609, 27783, 35721, 45927, 59049, 117649, 151263, 194481, 250047, 321489, 413343, 531441, 823543, 1058841, 1361367, 1750329, 2250423, 2893401, 3720087, 4782969
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OFFSET
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1,2
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LINKS
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FORMULA
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Sum_{n>=1} 1/a(n) = (7*9)/((7-1)*(9-1)) = 21/16. - Amiram Eldar, Sep 24 2020
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MATHEMATICA
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With[{nn=40}, Take[Union[7^First[#] 9^Last[#]&/@Tuples[Range[0, nn/4], 2]], nn]] (* Harvey P. Dale, Mar 06 2014 *)
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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