MATLAB: Is symsum operator giving me this answer

beginnerseriesSymbolic Math Toolboxsymsum

I am trying to find the sum of a series that goes like 20.^-20+19.^-19+…+1.^-1 Why is the answer such a massive number and why doesn't the formatting command work?
>> syms k
>> format shorteng
>> symsum(k.^(-1.*k),1,20)
ans =
32704926622076322328309250821720456282760440107801920978264646490630691318184399029563038640802578744801153948761512969045499776815021/25327407480969699779230080718754457246512673155164240823229977202846792179169322076528314293406963808740247706009600000000000000000000

Best Answer

The Symbolic Math Toolbox has its own way of formatting numbers: the vpa function:
syms k
S = symsum(k.^(-1.*k),1,20);
S = vpa(S, 5)
produces:
S =
1.2913
You can of course set the number of digits to whatever you want.
Also see the digits and double functions.
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