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A368723
a(n) = Product_{i=1..n, j=1..n, k=1..n} (i^4 + j^4 + k^4).
4
1, 3, 30180180096, 130911253854794147456410254996552949923277899497472
OFFSET
0,2
COMMENTS
Next term is too long to be included.
In general, for m>0, limit_{n->oo} (Product_{i=1..n, j=1..n, k=1..n} (i^m + j^m + k^m))^(1/(n^3)) / n^m = exp(Integral_{x=0..1, y=0..1, z=0..1} log(x^m + y^m + z^m) dz dy dx) = exp(Integral_{x=0..1, y=0..1} (log(1 + x^k + y^k) - k + k*hypergeom2F1(1/k, 1, (k+1)/k, -1/(x^k + y^k))) dy dx).
FORMULA
Limit_{n->oo} a(n)^(1/(n^3)) / n^4 = exp(Integral_{x=0..1, y=0..1, z=0..1} log(x^4 + y^4 + z^4) dz dy dx) = 0.3570458697635761757481417...
MATHEMATICA
Table[Product[i^4 + j^4 + k^4, {i, 1, n}, {j, 1, n}, {k, 1, n}], {n, 0, 5}]
CROSSREFS
Cf. A306594 (m=1), A324425 (m=2), A368722 (m=3).
Sequence in context: A036236 A235357 A260002 * A058447 A275939 A230810
KEYWORD
nonn
AUTHOR
Vaclav Kotesovec, Jan 04 2024
STATUS
approved