# [Tutor] value of 'e'

Shashwat Anand anand.shashwat at gmail.com
Tue Nov 24 12:47:06 CET 2009

```Followed by this discussion on Hacker
News<http://news.ycombinator.com/item?id=958323>I checked this
link <http://www.isotf.org/?page_value=13223> and was wondering how to
calculate value of 'e' <http://mathworld.wolfram.com/e.html> to a large
extent

as e = 1/0! + 1/1! +1/2! .... and so on...
so i wrote this:
>>> sum(1.0 / math.factorial(i) for i in range(100))
2.7182818284590455

It was not giving the precision that I wanted so I tried decimal module of
which I was not much aware of.

>>> decimal.getcontext().prec = 100
>>> sum(decimal.Decimal(str(1./math.factorial(decimal.Decimal(i)))) for i in
range(100))
Decimal('2.718281828459409995603699925637255290043107782360218523330012825771122202286299367023903783933889309')

Until now no problem
I matched the value of 'e' from
here<http://dl.dropbox.com/u/59605/ten_million_e.txt>
which claims it have 10 million digits of e
the first few digits of 'e' from there which doesn't match with the result I
got:
2.71828182845904523536028747135266249775724709369995957496696762772407

so i tried,
>>> sum(decimal.Decimal(str(1./math.factorial(decimal.Decimal(i)))) for i in
range(1000))
Traceback (most recent call last):
File "<input>", line 1, in <module>
File "<input>", line 2, in <genexpr>
OverflowError: long int too large to convert to float

And then i went clueless !!
How can it be done ?
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