This site is supported by donations to The OEIS Foundation.

From OeisWiki

There are two automatic email servers for identifying sequences:

• The first, sequences@research.att.com, does a simple look-up in the database. Send the message
  lookup 1 2 5 14 42 132 429         [no commas!]
  for example (with no Subject line). Up to 30 sequences can be submitted at the same time. This service is useful when the World Wide Web is congested.
  The email reply will tell you any sequences in the table (up to a limit of 50) that match your sequence.If the word "lookup" does not appear in your message, you will be sent the help file for this server.You can also retrieve sequences by A-number -- say
        lookup A12
        lookup A45
        lookup A129
  etc(However, you can't have both sequence lookups and A-number lookups in the same email message.)
• The second server does not just look up the sequence in the Encyclopedia, it will also apply a large number of algorithms in order to attempt to explain the sequence. Send a message to superseeker@research.att.comcontaining a line likelookup 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31(with no Subject line). The program will try VERY hard to find an explanation. Only one request may be submitted at a time, and (since this program does some serious computing), only one request per user per hour please. If there is no lookup line you will receive the help file. A French version of the help file is also available. (This is not as up-to-date as the English version though.)

These servers are described in more detail in an article in the Electronic Journal of Combinatorics (Feature #F1 in Volume 1 ); in the book; and in the help files mentioned above. They have also been written up in several magazines.