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A025723
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Index of 7^n within sequence of numbers of form 5^i*7^j.
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1
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1, 3, 6, 10, 15, 22, 30, 39, 49, 60, 73, 87, 102, 118, 135, 154, 174, 195, 217, 240, 265, 291, 318, 346, 376, 407, 439, 472, 506, 542, 579, 617, 656, 696, 738, 781, 825, 870, 916, 964, 1013, 1063, 1114, 1166, 1220, 1275, 1331, 1388, 1447, 1507, 1568, 1630, 1693
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internal format)
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OFFSET
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0,2
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LINKS
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FORMULA
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a(n) = 1 + Sum_{k=1..n} ceiling(k*log_5(7)). - Robert Israel, Nov 16 2016
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MAPLE
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ListTools:-PartialSums([1, seq(ceil(k*log[5](7)), k=1..100)]); # Robert Israel, Nov 16 2016
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MATHEMATICA
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Table[1 + Sum[Ceiling[k Log[5, 7]], {k, n}], {n, 0, 52}] (* Michael De Vlieger, Nov 16 2016 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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