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A085392
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a(n) = largest prime divisor of n, or 1 if n is 1 or a prime.
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10
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1, 1, 1, 2, 1, 3, 1, 2, 3, 5, 1, 3, 1, 7, 5, 2, 1, 3, 1, 5, 7, 11, 1, 3, 5, 13, 3, 7, 1, 5, 1, 2, 11, 17, 7, 3, 1, 19, 13, 5, 1, 7, 1, 11, 5, 23, 1, 3, 7, 5, 17, 13, 1, 3, 11, 7, 19, 29, 1, 5, 1, 31, 7, 2, 13, 11, 1, 17, 23, 7, 1, 3, 1, 37, 5, 19, 11, 13, 1, 5, 3, 41, 1, 7, 17, 43, 29, 11, 1, 5, 13
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OFFSET
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1,4
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LINKS
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FORMULA
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MAPLE
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A085392 := proc(n) max( op(numtheory[divisors](n) minus {n})) ; A006530(%) ;
end proc:
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MATHEMATICA
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PrimeFactors[n_] := Flatten[ Table[ # [[1]], {1}] & /@ FactorInteger[n]]; f[n_] := Block[{gpd = Divisors[n][[ -2]]}, If[gpd == 1, 1, PrimeFactors[gpd][[ -1]] ]]; Table[ If[n == 1, 1, f[n]], {n, 1, 95}]
Join[{1}, Table[FactorInteger[Divisors[n][[-2]]][[-1, 1]], {n, 2, 120}]] (* Harvey P. Dale, Jul 02 2019 *)
a[n_] := If[CompositeQ[n], FactorInteger[n][[-1, 1]], 1]; Array[a, 100] (* Amiram Eldar, Jun 19 2022 *)
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PROG
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(Haskell)
(PARI) gpd(n) = if (n==1, 1, n/factor(n)[1, 1]);
gpf(n) = if (n==1, 1, vecmax(factor(n)[, 1]));
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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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Definition corrected by N. J. A. Sloane, Jul 02 2019. Also deleted an incorrect comment.
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STATUS
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approved
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