OFFSET
1,2
EXAMPLE
For n = 3: a 63-ball of radius 2 has a volume of 0.91035..., while a 63-ball of radius 3 has a volume of 112969101106.64166... Since 63 is the least number of dimensions where a ball with unit volume has a radius >= 3, a(3) = 63.
MATHEMATICA
a[1]=1; a[n_]:=a[n] = Block[{k = a[n-1]}, While[Ceiling[(Pi^(-k/2) Gamma[1 + k/2])^(1/k)] < n, k++]; k]; Array[a, 20] (* Giovanni Resta, Apr 29 2017 *)
PROG
(PARI) volume(n, r) = ((Pi^(n/2))/(gamma(1+n/2)))*r^n
a285481(n) = my(k=1); while(1, if(volume(n, k) >= 1, return(k)); k++)
a(n) = my(k=1); while(1, if(a285481(k) >= n, return(k)); k++)
CROSSREFS
KEYWORD
nonn
AUTHOR
Felix Fröhlich, Apr 28 2017
EXTENSIONS
a(36)-a(42) from Giovanni Resta, Apr 29 2017
STATUS
approved