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 A065958 a(n) = n^2*Product_{distinct primes p dividing n} (1+1/p^2). 12
 1, 5, 10, 20, 26, 50, 50, 80, 90, 130, 122, 200, 170, 250, 260, 320, 290, 450, 362, 520, 500, 610, 530, 800, 650, 850, 810, 1000, 842, 1300, 962, 1280, 1220, 1450, 1300, 1800, 1370, 1810, 1700, 2080, 1682, 2500, 1850, 2440, 2340, 2650, 2210 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The sequence may be considered as psi_2, a generalization of Dedekind's Psi Function, where psi_1 is A001615. - Enrique Pérez Herrero, Jul 06 2011 REFERENCES József Sándor, Geometric Theorems, Diophantine Equations, and Arithmetic Functions, American Research Press, Rehoboth 2002, pp. 193. LINKS E. Pérez Herrero, Table of n, a(n) for n = 1..10000 F. A. Lewis and others, Problem 4002, Amer. Math. Monthly, Vol. 49, No. 9, Nov. 1942, pp. 618-619. FORMULA Multiplicative with a(p^e) = p^(2*e) + p^(2*e-2). - Vladeta Jovovic, Dec 09 2001 a(n) = n^2 * Sum_{d|n} mu(d)^2/d^2 - Benoit Cloitre, Apr 07 2002 a(n) = Sum_{d|n} mu(d)^2*d^2. - Joerg Arndt, Jul 06 2011 Inverse Euler transform of n*A156733(n). - Paul D. Hanna and Vladeta Jovovic, Feb 14 2009 From Enrique Pérez Herrero, Aug 22 2010: (Start) a(n) = J_4(n)/(phi(n)*psi(n)) = A059377(n)/(A001615(n)*A000010(n)) a(n) = J_4(n)/J_2(n) = A059377(n)/A007434(n), where J_k is the k-th Jordan Totient Function. (End) Dirichlet g.f.: zeta(s)*zeta(s-2)/zeta(2s). Dirichlet convolution of A008966 and A000290. - R. J. Mathar, Apr 10 2011 G.f.: Sum_{k>=1} mu(k)^2*x^k*(1 + x^k)/(1 - x^k)^3. - Ilya Gutkovskiy, Oct 24 2018 Sum_{k>=1} 1/a(k) = Product_{primes p} (1 + p^2/(p^4 - 1)) = 1.5421162831401587416523241690601522041445615542162573163112157073779258386... - Vaclav Kotesovec, Sep 19 2020 a(n) = Sum_{d|n} d*phi(d)*psi(n/d). - Ridouane Oudra, Jan 01 2021 From Richard L. Ollerton, May 07 2021: (Start) a(n) = Sum_{k=1..n} psi(gcd(n,k))*n/gcd(n,k), where psi(n) = A001615(n). a(n) = Sum_{k=1..n} psi(n/gcd(n,k))*gcd(n,k)*phi(gcd(n,k))/phi(n/gcd(n,k)). (End) MAPLE A065958 := proc(n) local i, j, k, t1, t2, t3; t1 := ifactors(n)[2]; t2 := n^2*mul((1+1/(t1[i][1])^2), i=1..nops(t1)); end; MATHEMATICA JordanTotient[n_, k_:1]:=DivisorSum[n, #^k*MoebiusMu[n/# ]&]/; (n>0)&&IntegerQ[n]; A065958[n_]:=JordanTotient[n, 4]/JordanTotient[n, 2]; (* Enrique Pérez Herrero, Aug 22 2010 *) f[p_, e_] := p^(2*e) + p^(2*(e-1)); a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* Amiram Eldar, Oct 12 2020 *) PROG (PARI) for(n=1, 100, print1(n*sumdiv(n, d, moebius(d)^2/d^2), ", ")) (PARI) a(n)=sumdiv(n, d, moebius(n/d)^2*d^2); /* Joerg Arndt, Jul 06 2011 */ CROSSREFS Cf. A000010, A001615, A007434, A065959, A065960, A156733, A301978, A301980, A321973. Sequence in context: A072703 A086761 A045191 * A065969 A306775 A027884 Adjacent sequences:  A065955 A065956 A065957 * A065959 A065960 A065961 KEYWORD nonn,mult,easy AUTHOR N. J. A. Sloane, Dec 08 2001 STATUS approved

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Last modified January 20 13:55 EST 2022. Contains 350472 sequences. (Running on oeis4.)