Carol Vorderman is leaving Countdown later this year
Channel 4 is launching a search to find a man or a woman to replace Carol Vorderman when she leaves Countdown later this year.
Producers are looking for a maths whizz with "charm and charisma" to appear on the popular show from January 2009.
Vorderman, 47, announced in July she planned to step down from the show after 25 years.
Interested applicants - who must have "excellent" numeric and literacy skills - can apply on the Channel 4 website.
Helen Warner, head of daytime at Channel 4, said: "We realise that Carol's shoes are extremely difficult ones to fill, as she has done such an amazing job on Countdown over the past 25 years.
"However, just as we found Carol through an ad in a local paper, we really hope we can do the same again and find another outstanding mathematical mastermind.
"We know many Countdown viewers have great heads for numbers, so we are looking forward to seeing how talented they really are!"
Short-listed applicants will be invited to attend auditions with Countdown producers. The closing date to apply is 19 September 2008.
Vorderman was part of the original team on the words-and-numbers game show, which was the first programme to be broadcast when Channel 4 began in 1982.
She started as the maths "expert" who would check contestants' sums in the numbers rounds, but took on extra duties to become a sidekick to presenter Richard Whiteley.
Countdown's current host, Des O'Connor, has announced he will leave the show in November after presenting more than 500 editions. His replacement will be announced later this year.