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A033196 a(n) = n^3*Product_{p|n} (1 + 1/p). 3

%I #28 Sep 20 2020 03:44:29

%S 1,12,36,96,150,432,392,768,972,1800,1452,3456,2366,4704,5400,6144,

%T 5202,11664,7220,14400,14112,17424,12696,27648,18750,28392,26244,

%U 37632,25230,64800,30752,49152,52272,62424,58800,93312,52022,86640

%N a(n) = n^3*Product_{p|n} (1 + 1/p).

%H T. D. Noe, <a href="/A033196/b033196.txt">Table of n, a(n) for n=1..1000</a>

%F Dirichlet g.f.: zeta(s-2)*zeta(s-3)/zeta(2*s-4).

%F a(n) = n^2*A001615(n) = n *A000082(n).

%F Multiplicative with a(p^e) = p^e*p^(2*e-1)*(p+1). - _Vladeta Jovovic_, Nov 16 2001

%F a(n) = sum_{d|n} mu(d)*sigma(n^3/d^2). - _Benoit Cloitre_, Feb 16 2008

%F a(n) = A001615(n^3) = A001615(n^k)/n^(k-3), with k>2. - _Enrique Pérez Herrero_, Mar 06 2012

%F Sum_{k=1..n} a(k) ~ 15*n^4 / (4*Pi^2). - _Vaclav Kotesovec_, Feb 01 2019

%F Sum_{k>=1} 1/a(k) = Product_{primes p} (1 + p/((p+1)*(p^3-1))) = 1.1392293101137663761606045655621290749920977339371831842000361508083066155... - _Vaclav Kotesovec_, Sep 20 2020

%t a[n_] := n*DivisorSum[n, MoebiusMu[n/#] DivisorSigma[1, #^2]&]; Array[a, 40] (* _Jean-François Alcover_, Dec 02 2015 *)

%o (PARI) a(n)=direuler(p=2,n,(1+p^2*X)/(1-p^3*X))[n]

%o (PARI) a(n)=sumdiv(n,d,moebius(d)*sigma(n^3/d^2)) \\ _Benoit Cloitre_, Feb 16 2008

%K nonn,easy,mult

%O 1,2

%A _N. J. A. Sloane_.

%E Additional comments from _Michael Somos_, May 19 2000

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Last modified March 28 05:39 EDT 2024. Contains 371235 sequences. (Running on oeis4.)