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A264441
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Length of row n of the irregular triangle A133995 (positive integers <= n which are neither divisors of n nor coprime to n).
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2
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1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 3, 1, 5, 4, 4, 1, 7, 1, 7, 6, 9, 1, 9, 3, 11, 6, 11, 1, 15, 1, 11, 10, 15, 8, 16, 1, 17, 12, 17, 1, 23, 1, 19, 16, 21, 1, 23, 5, 25, 16, 23, 1, 29, 12, 25, 18, 27, 1, 33, 1, 29, 22, 26, 14, 39, 1, 31, 22, 39, 1
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OFFSET
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1,10
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LINKS
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FORMULA
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a(1) = 1, a(4) = 1 and a(n) = 1 if n is a prime (n from A000040) else a(n) = A045763(n).
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MAPLE
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seq(max(1, n - numtheory:-tau(n) - numtheory:-phi(n) + 1), n=1..100); # Robert Israel, Jan 28 2016
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MATHEMATICA
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a[1] = a[4] = 1; a[n_] := If[PrimeQ[n], 1, n + 1 - DivisorSigma[0, n] - EulerPhi[n]]; Array[a, 100] (* Jean-François Alcover, Jan 18 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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STATUS
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approved
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