Using the result of a previously evaluated cell

edit

For a previously evaluated cell in a Jupyter notebook, you can use Out[...], replacing ... by the number of the output cell you want to refer to.

Example.

In[1]: 1 + 1
Out[1]: 2
In[2]: 20 + 20
Out[2]: 40
In[3]: Out[1] * 5
Out[3]: 10

EDIT (2018-01-05).

Note that this also works in the Sage REPL (read-eval-print loop), or "command-line interface", ie, using Sage in a terminal. The reason is that, like Jupyter, it uses IPython behind the scenes. The difference is that the cell numbers are not displayed there... They still exist though.

Example:

$ sage -v
SageMath version 8.1, Release Date: 2017-12-07
$ sage -q
sage: 1 + 1
2
sage: 20 + 20
40
sage: Out[1] * 5
10

If you want to get one of the last few cells and want to figure out what is the current number, you could ask the length of In or the length of Out.

Example:

$ sage -v
SageMath version 8.1, Release Date: 2017-12-07
$ sage -q
sage: 1 + 1
2
sage: 9 * 9
81
sage: len(Out)
2
sage: Out[2]
81

There might be a way of making Sage display the numbering of the input and output... But I don't know how to do it!