This is an unusual sequence mentioned on the Math Fun Mailing list. It does not quite fit the format of regular OEIS entries, but is too interesting to be forgotten. - N. J. A. Sloane, Mar 29 2009
The definition arises from the Fourier series for the Snowflake curve.
..................................................................
.............................. inf ...............................
.............................. ==== ............ m ...............
............................ k \ ....... %pi (k 2..- 5) ..... n ..
....................... (- 1).. > .. tan(--------------) (- 1) ...
............. inf ............ / ............ n + m ..............
............. ==== ........... ==== ........ 2 ...................
..... 5 m - 1 \ .............. n = 1 .............................
.. 3 2 ....... > ...... --------------------------------------- ..
............. / .................................... m ...........
............. ==== .......... m ... 3 ... 10 %pi (k 2 .- 5) ......
............. k = - inf . (k 2..- 5)..csc(-----------------) .....
................................................ 2 m .............
............................................... 2 ................
.. ------------------------------------------------------------ ..
........................... 3 ... 5 %pi ..........................
........................ %pi..csc(-----) .........................
................................... m ............................
.................................. 2 .............................
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