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A292785
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Number of odd squarefree semiprimes < 10^n.
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2
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0, 16, 194, 1932, 18181, 168330, 1555366, 14424896, 134429269, 1258812629, 11840308472, 111817802539, 1059796159358, 10076977878935, 96091981692305, 918679869869451, 8803388128870716, 84537081067757934, 813340036390023775, 7838825925395981969, 75669246174605279757
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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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EXAMPLE
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a(2)=16 because there are 16 squarefree odd semiprimes < 10^2: 15=3*5, 21=3*7, 33=3*11, 35=5*7, 39=3*13, 51=3*17, 55=5*11, 57=3*19, 65=5*13, 69=3*23, 77=7*11, 85=5*17, 87=3*29, 91=7*13, 93=3*31, 95=5*19.
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MATHEMATICA
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-1 + Accumulate@ Table[Count[Range[10^n + 1, 10^(n + 1) - 1, 2], _?(And[ SquareFreeQ@ #, PrimeNu[#] == 2] &)], {n, 0, 5}] (* Michael De Vlieger, Oct 10 2017 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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