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A038991
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Number of sublattices of index n in generic 4-dimensional lattice.
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12
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1, 15, 40, 155, 156, 600, 400, 1395, 1210, 2340, 1464, 6200, 2380, 6000, 6240, 11811, 5220, 18150, 7240, 24180, 16000, 21960, 12720, 55800, 20306, 35700, 33880, 62000, 25260, 93600, 30784, 97155, 58560, 78300, 62400, 187550, 52060, 108600, 95200, 217620, 70644, 240000, 81400
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OFFSET
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1,2
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REFERENCES
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M. Baake, "Solution of coincidence problem...", in R. V. Moody, ed., Math. of Long-Range Aperiodic Order, Kluwer 1997, pp. 9-44.
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LINKS
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FORMULA
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f(Q, n) = Sum_{d|n} d*f(Q-1, d); here Q=4.
Dirichlet g.f.: zeta(s)*zeta(s-1)*zeta(s-2)*zeta(s-3).
Multiplicative with a(p^e) = Product_{k=1..3} (p^(e+k)-1)/(p^k-1).
Sum_{k=1..n} a(k) ~ Pi^6 * Zeta(3) * n^4 / 2160. - Vaclav Kotesovec, Feb 01 2019
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MATHEMATICA
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f[p_, e_] := Product[(p^(e + k) - 1)/(p^k - 1), {k, 1, 3}]; a[1] = 1; a[n_] := Times @@ (f @@@ FactorInteger[n]); Array[a, 100] (* Amiram Eldar, Aug 29 2019 *)
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PROG
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(PARI) a(n)=sumdiv(n, x, x * sumdiv(x, y, y * sumdiv(y, z, z ) ) ); /* Joerg Arndt, Oct 07 2012 */
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CROSSREFS
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KEYWORD
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nonn,mult
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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