The seed is different for each token, and is loaded into the corresponding RSA SecurID server (RSA Authentication Manager, formerly ACE/Server) as the tokens are purchased 1. So, it may have something related to the RSA public key algorithm.
Citing on Wiki The RSA SecurID authentication mechanism consists of a "token" either hardware (e.g. a USB dongle) or software (a soft token) which is assigned to a computer user and which generates an authentication code at fixed intervals (usually 60 seconds) using a built-in.
UPDATE : Thanks to eyaler, there are no any public/private keys in classic SecurID; they are based on "shared secret not on asymmetric algorithm. Wikipedia says, that variant of AES-128 is used to generate token codes from the museum nana mizuki iso secret key seed.
Little known about real internals of SecurID (security by obscurity but there are some analysis, e.g. initial securid analysis and more at bottom of SecurID page in wikipedia. Also, hardware tokens are Tamper resistant so it is almost impossible to duplicate stolen token.
The secret key is encoded into key at factory).