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A070777
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a(1) = 1; a(n) = (largest prime factor of n) - 1.
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11
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1, 1, 2, 1, 4, 2, 6, 1, 2, 4, 10, 2, 12, 6, 4, 1, 16, 2, 18, 4, 6, 10, 22, 2, 4, 12, 2, 6, 28, 4, 30, 1, 10, 16, 6, 2, 36, 18, 12, 4, 40, 6, 42, 10, 4, 22, 46, 2, 6, 4, 16, 12, 52, 2, 10, 6, 18, 28, 58, 4, 60, 30, 6, 1, 12, 10, 66, 16, 22, 6, 70, 2, 72, 36, 4, 18, 10, 12, 78, 4, 2, 40, 82, 6
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OFFSET
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1,3
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COMMENTS
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Also a(n) = Euler Phi of largest prime factor of n (previous name).
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LINKS
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FORMULA
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EXAMPLE
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102 = 2*3*17, so a(102) = 17 - 1 = 16.
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MAPLE
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with(numtheory): A070777 := n -> `if`(n=1, 1, phi(max(op(factorset(n))))): # Peter Luschny, Oct 23 2010
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MATHEMATICA
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a[n_] := EulerPhi[Last[FactorInteger[n]][[1]]]; Table[a[n], {n, 1, 200}] (* José María Grau Ribas, Feb 21 2010 *)
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PROG
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(PARI) a(n) = if (n==1, 1, vecmax(factor(n)[, 1]) - 1); \\ after A006530; Michel Marcus, May 19 2015
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CROSSREFS
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KEYWORD
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easy,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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