OFFSET
2,1
COMMENTS
Lim_{n->inf.} i_n/i_(n-1) approaches Pi. e.g. 2791558571/8885799011=~3.141598593...
See A108925. Analytical Pi (for n>=4 but here n>10^6 say),(n=1 2 3...n). Take n straight lines monotonically increasing in length by one and join them end to end; the last to the first. When the enclosed area is at its maximum every vertex will lie on the circumference of a circle the diameter of which divided into Triangular(n) equals Pi.
There is an interesting benchmark when n=8. The radius calculated using Pi equals 5.7296...; one tenth of the number of degrees in a radian. The radius when plotted as a drawing is very near to six and, tentatively, this could be ten times a constant near to point six.
It appears that a(2n-1) taken when rounded down (rather than to the nearest integer) is equal to A100594(n). - Terry D. Grant, May 28 2017
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 2..1000
EXAMPLE
a(n) = d where d is the integer divisor of Pi^n for even n and (Pi^n)-ne for odd n having a solution closest to Zeta(n).
a(2) = 6 then (Pi^2)/6 = Zeta(2); a(3)=19, (Pi^3-3e)/19 approx = Zeta(3); a(4)=90, (Pi^4)/90 = Zeta(4); and the only special case the author has found where ((Pi^4)-4e)/80 approx = Zeta(4).
MATHEMATICA
f[n_] := Round@If[EvenQ@n, Pi^n/Zeta@n, (Pi^n - n*E)/Zeta@n]; Table[ f@n, {n, 2, 26}] (* Robert G. Wilson v, Nov 18 2005 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Marco Matosic, Nov 16 2005
EXTENSIONS
Corrected and extended by Robert G. Wilson v, Nov 18 2005
Corrections from Marco Matosic, Mar 27 2006
Definition clarified by Omar E. Pol, Jan 02 2009
STATUS
approved