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A036322
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Composite numbers whose prime factors contain no digits other than 6 and 7.
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2
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49, 343, 469, 2401, 3283, 4489, 4739, 16807, 22981, 31423, 33173, 45359, 117649, 160867, 219961, 232211, 300763, 317513, 458329, 474439, 536669, 537439, 823543, 1126069, 1539727, 1625477, 2105341, 2222591, 3039053, 3208303, 3321073
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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COMMENTS
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LINKS
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FORMULA
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Sum_{n>=1} 1/a(n) = Product_{p in A020469} (p/(p - 1)) - Sum_{p in A020469} 1/p - 1 = 0.0268448443... . - Amiram Eldar, May 22 2022
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CROSSREFS
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KEYWORD
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nonn,easy,base
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AUTHOR
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STATUS
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approved
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