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A034448
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usigma(n) = sum of unitary divisors of n (divisors d such that gcd(d, n/d)=1); also called UnitarySigma(n).
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256
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1, 3, 4, 5, 6, 12, 8, 9, 10, 18, 12, 20, 14, 24, 24, 17, 18, 30, 20, 30, 32, 36, 24, 36, 26, 42, 28, 40, 30, 72, 32, 33, 48, 54, 48, 50, 38, 60, 56, 54, 42, 96, 44, 60, 60, 72, 48, 68, 50, 78, 72, 70, 54, 84, 72, 72, 80, 90, 60, 120, 62, 96, 80, 65, 84, 144, 68, 90, 96, 144
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OFFSET
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1,2
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COMMENTS
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Row sums of the triangle in A077610. - Reinhard Zumkeller, Feb 12 2002
Multiplicative with a(p^e) = p^e+1 for e>0. - Franklin T. Adams-Watters, Sep 11 2005
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LINKS
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T. D. Noe, Table of n, a(n) for n = 1..10000
Steven R. Finch, Unitarism and Infinitarism, February 25, 2004. [Cached copy, with permission of the author]
Carl Pomerance and Hee-Sung Yang, Variant of a theorem of Erdos on the sum-of-proper-divisors function, Math. Comp., to appear (2014).
Tim Trudgian, The sum of the unitary divisor function, Publications de l'Institut Mathématique 2015 Vol. 97, Issue 111, pp. 175-180.
Eric Weisstein's World of Mathematics, Unitary Divisor Function
Wikipedia, Unitary divisor
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FORMULA
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If n = Product p_i^e_i, usigma(n) = Product (p_i^e_i + 1). - Vladeta Jovovic, Apr 19 2001
Dirichlet generating function: zeta(s)*zeta(s-1)/zeta(2s-1). - Franklin T. Adams-Watters, Sep 11 2005
Conjecture: a(n) = sigma(n^2/rad(n))/sigma(n/rad(n)), where sigma = A000203 and rad = A007947. - Velin Yanev, Aug 20 2017
From Amiram Eldar, May 29 2020: (Start)
Sum_{d|n, gcd(d, n/d) = 1} a(d) * (-1)^omega(n/d) = n.
a(n) <= sigma(n) = A000203(n), with equality if and only if n is squarefree (A005117). (End)
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EXAMPLE
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Unitary divisors of 12 are 1, 3, 4, 12. Or, 12=3*2^2 hence usigma(12)=(3+1)*(2^2+1)=20.
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MAPLE
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A034448 := proc(n) local ans, i:ans := 1: for i from 1 to nops(ifactors(n)[ 2 ]) do ans := ans*(1+ifactors(n)[ 2 ][ i ][ 1 ]^ifactors(n)[ 2 ] [ i ] [ 2 ]): od: RETURN(ans) end:
a := proc(n) local i; numtheory[divisors](n); select(d -> igcd(d, n/d)=1, %); add(i, i=%) end; # Peter Luschny, May 03 2009
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MATHEMATICA
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usigma[n_] := Block[{d = Divisors[n]}, Plus @@ Select[d, GCD[ #, n/# ] == 1 &]]; Table[ usigma[n], {n, 71}] (* Robert G. Wilson v, Aug 28 2004 *)
Table[DivisorSum[n, # &, CoprimeQ[#, n/#] &], {n, 70}] (* Michael De Vlieger, Mar 01 2017 *)
usigma[n_] := If[n == 1, 1, Times @@ (1 + Power @@@ FactorInteger[n])]; Array[usigma, 100] (* faster since avoids generating divisors, Giovanni Resta, Apr 23 2017 *)
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PROG
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(PARI) A034448(n)=sumdiv(n, d, if(gcd(d, n/d)==1, d)) \\ Rick L. Shepherd
(PARI) A034448(n) = {my(f=factorint(n)); prod(k=1, #f[, 2], f[k, 1]^f[k, 2]+1)} \\ Andrew Lelechenko, Apr 22 2014
(PARI) a(n)=sumdivmult(n, d, if(gcd(d, n/d)==1, d)) \\ Charles R Greathouse IV, Sep 09 2014
(Haskell) a034448 = sum . a077610_row -- Reinhard Zumkeller, Feb 12 2012
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CROSSREFS
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Cf. A000203, A034444, A034460, A047994, A048250, A064000, A064609.
Cf. A063937 (squares > 1).
Cf. A188999, A301981, A301982.
Sequence in context: A103402 A154664 A191750 * A331107 A069184 A181549
Adjacent sequences: A034445 A034446 A034447 * A034449 A034450 A034451
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KEYWORD
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nonn,easy,nice,mult
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AUTHOR
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N. J. A. Sloane, Dec 11 1999
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EXTENSIONS
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More terms from Erich Friedman
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STATUS
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approved
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