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A161946
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Odd part of sum of unitary divisors of n.
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2
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1, 3, 1, 5, 3, 3, 1, 9, 5, 9, 3, 5, 7, 3, 3, 17, 9, 15, 5, 15, 1, 9, 3, 9, 13, 21, 7, 5, 15, 9, 1, 33, 3, 27, 3, 25, 19, 15, 7, 27, 21, 3, 11, 15, 15, 9, 3, 17, 25, 39, 9, 35, 27, 21, 9, 9, 5, 45, 15, 15, 31, 3, 5, 65, 21, 9, 17, 45, 3, 9, 9, 45, 37, 57, 13, 25, 3, 21, 5, 51, 41, 63, 21, 5, 27
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OFFSET
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1,2
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COMMENTS
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Since a(n) < n for any odd n > 1, iterating this function always leads to 1.
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LINKS
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FORMULA
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Multiplicative with a(p^e) = oddpart(p^e+1), where oddpart(n) = A000265(n) is the largest odd divisor of n.
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MATHEMATICA
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Table[NestWhile[#/2 &, DivisorSum[n, # &, CoprimeQ[#, n/#] &], EvenQ@ # &], {n, 85}] (* Michael De Vlieger, Nov 23 2017 *)
a[n_] := Times @@ ((#/2^IntegerExponent[#, 2]) & /@ (1 + Power @@@ FactorInteger[n])); Array[a, 100] (* Amiram Eldar, Oct 26 2023 *)
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PROG
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(PARI) oddpart(n)=n/2^valuation(n, 2)
a(n)=local(fm, r); fm=factor(n); r=1; for(k=1, matsize(fm)[1], r*=oddpart(fm[k, 1]^fm[k, 2]+1)); r
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CROSSREFS
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KEYWORD
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easy,mult,nonn
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AUTHOR
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STATUS
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approved
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