Alan Turing's Paper - Computable Numbers - Decision Problem (ENTSCHEIDUNGSPROBLEM)

Many people consider this as the beginning of algorithms and digital computing-  the Alan Turing paper on computable numbers published in 1936.

Read it here.

Some of its popular sentences are:
 'a number is computable if its decimal can be written down by a machine'
&
'We have said that the computable numbers are those whose decimals are calculable by finite means. This requires rather more explicit definition. No real attempt will be made to justify the definitions given until we reach § 9. For the present I shall only say that the justification lies in the fact that the human memory is necessarily limited'