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A078401
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Triangle read by rows: T(n,k) = number of numbers <= k that are coprime to n, 1<=k<=n.
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2
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1, 1, 1, 1, 2, 2, 1, 1, 2, 2, 1, 2, 3, 4, 4, 1, 1, 1, 1, 2, 2, 1, 2, 3, 4, 5, 6, 6, 1, 1, 2, 2, 3, 3, 4, 4, 1, 2, 2, 3, 4, 4, 5, 6, 6, 1, 1, 2, 2, 2, 2, 3, 3, 4, 4, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 10, 1, 1, 1, 1, 2, 2, 3, 3, 3, 3, 4, 4, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 12, 1, 1, 2, 2, 3, 3, 3, 3, 4, 4, 5
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OFFSET
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1,5
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COMMENTS
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T(n,1) = 1; T(n,n) = phi(n), where phi is Euler's totient function (A000010); for p prime: T(p,i) = i for 1<=i<p and T(p,p) = p-1.
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LINKS
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FORMULA
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T(n,k) = Sum{mu(d)*floor(k/d): n mod d = 0}, where mu is the Moebius Function (A008683).
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EXAMPLE
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1,
1, 1,
1, 2, 2,
1, 1, 2, 2,
1, 2, 3, 4, 4,
1, 1, 1, 1, 2, 2,
1, 2, 3, 4, 5, 6, 6,
1, 1, 2, 2, 3, 3, 4, 4,
1, 2, 2, 3, 4, 4, 5, 6, 6,
1, 1, 2, 2, 2, 2, 3, 3, 4, 4,
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MAPLE
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a := 0 ;
for j from 1 to k do
if igcd(j, n) = 1 then
a := a+1 ;
end if;
end do:
a ;
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MATHEMATICA
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T[n_, k_] := Count[Range[k], d_ /; CoprimeQ[n, d]];
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CROSSREFS
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KEYWORD
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AUTHOR
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EXTENSIONS
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Thanks to Duc Ngo Minh (ducnm0(AT)gmail.com) who noticed an error in the formula; corrected by Reinhard Zumkeller, Mar 01 2009
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STATUS
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approved
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