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A343802
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Least positive integer k such that Sum_{i=1..k} phi(i) >= 10^n.
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1
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1, 5, 18, 57, 181, 573, 1814, 5736, 18138, 57357, 181380, 573574, 1813799, 5735737, 18137993, 57357372, 181379937, 573573721, 1813799364, 5735737209, 18137993642, 57357372095, 181379936423, 573573720955, 1813799364234, 5735737209545, 18137993642342, 57357372095455
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OFFSET
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0,2
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COMMENTS
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Least integer k such that A002088(k) >= 10^n.
Since A002088(k) = (3*k^2)/(Pi^2) + O(k log k), the digits of a(n) for n even (resp. odd) approach the decimal digits of Pi/sqrt(3)=1.8137993642342... and Pi*sqrt(10/3)=5.7357372095454... resp.
Conjecture: For n even, either a(n) = floor(Pi/sqrt(3)*10^(n/2)) or a(n) = floor(Pi/sqrt(3)*10^(n/2))+1. For n odd, either a(n) = floor(Pi*sqrt(10/3)*10^((n-1)/2)) or a(n) = floor(Pi*sqrt(10/3)*10^((n-1)/2))+1.
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LINKS
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PROG
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(Python)
from sympy import totient
s, c = 0, 0
while s < 10**n:
c += 1
s += totient(c)
return c
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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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