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a(n) = n^6 * Sum_{d^2|n} 1 / d^6.
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%I #28 Nov 14 2022 01:39:36

%S 1,64,729,4160,15625,46656,117649,266240,532170,1000000,1771561,

%T 3032640,4826809,7529536,11390625,17043456,24137569,34058880,47045881,

%U 65000000,85766121,113379904,148035889,194088960,244156250,308915776,387951930,489419840,594823321,729000000

%N a(n) = n^6 * Sum_{d^2|n} 1 / d^6.

%H Seiichi Manyama, <a href="/A351604/b351604.txt">Table of n, a(n) for n = 1..10000</a>

%F Multiplicative with a(p^e) = p^6*(p^(6*e) - p^(6*floor((e-1)/2)))/(p^6 - 1). - _Sebastian Karlsson_, Feb 25 2022

%F Sum_{k=1..n} a(k) ~ c * n^7, where c = zeta(8)/7 = Pi^8/66150 = 0.143439... . - _Amiram Eldar_, Nov 13 2022

%t f[p_, e_] := p^6*(p^(6*e) - p^(6*Floor[(e - 1)/2]))/(p^6 - 1); a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 30] (* _Amiram Eldar_, Nov 13 2022 *)

%o (PARI) a(n) = n^6*sumdiv(n, d, if (issquare(d), 1/d^3)); \\ _Michel Marcus_, Feb 15 2022

%Y Sequences of the form n^k * Sum_{d^2|n} 1/d^k for k = 0..10: A046951 (k=0), A340774 (k=1), A351600 (k=2), A351601 (k=3), A351602 (k=4), A351603 (k=5), this sequence (k=6), A351605 (k=7), A351606 (k=8), A351607 (k=9), A351608 (k=10).

%Y Cf. A013666.

%K nonn,mult

%O 1,2

%A _Wesley Ivan Hurt_, Feb 14 2022