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A256691
From fourth root of Riemann zeta function: form Dirichlet series Sum b(n)/n^x whose fourth power is zeta function; sequence gives denominator of b(n).
11
1, 4, 4, 32, 4, 16, 4, 128, 32, 16, 4, 128, 4, 16, 16, 2048, 4, 128, 4, 128, 16, 16, 4, 512, 32, 16, 128, 128, 4, 64, 4, 8192, 16, 16, 16, 1024, 4, 16, 16, 512, 4, 64, 4, 128, 128, 16, 4, 8192, 32, 128, 16, 128, 4, 512, 16, 512, 16, 16, 4, 512, 4, 16, 128, 65536, 16, 64, 4, 128, 16, 64, 4, 4096, 4, 16, 128, 128, 16, 64, 4, 8192, 2048, 16, 4, 512, 16, 16, 16, 512, 4, 512, 16, 128, 16, 16, 16, 32768, 4, 128, 128, 1024
OFFSET
1,2
COMMENTS
Dirichlet g.f. of A256690(n)/A256691(n) is (zeta (x))^(1/4).
Formula holds for general Dirichlet g.f. zeta(x)^(1/k) with k = 1, 2, ...
LINKS
FORMULA
with k = 4;
zeta(x)^(1/k) = Sum_{n>=1} b(n)/n^x;
c(1,n)=b(n); c(k,n) = Sum_{d|n} c(1,d)*c(k-1,n/d), k>1;
Then solve c(k,n) = 1 for b(m);
a(n) = denominator(b(n)).
EXAMPLE
b(1), b(2), ... = 1, 1/4, 1/4, 5/32, 1/4, 1/16, 1/4, 15/128, 5/32, 1/16, 1/4, 5/128, 1/4, 1/16, 1/16, 195/2048, ...
MATHEMATICA
k = 4;
c[1, n_] = b[n];
c[k_, n_] := DivisorSum[n, c[1, #1]*c[k - 1, n/#1] & ]
nn = 100; eqs = Table[c[k, n] == 1, {n, 1, nn}];
sol = Solve[Join[{b[1] == 1}, eqs], Table[b[i], {i, 1, nn}], Reals];
t = Table[b[n], {n, 1, nn}] /. sol[[1]];
num = Numerator[t] (* A256690 *)
den = Denominator[t] (* A256691 *)
CROSSREFS
Cf. A046643/A046644 (k=2), A256688/A256689 (k=3), A256690/A256691 (k=4), A256692/A256693 (k=5).
Sequence in context: A337447 A239601 A196131 * A120030 A138504 A002611
KEYWORD
nonn,frac,mult
AUTHOR
Wolfgang Hintze, Apr 08 2015
STATUS
approved