Dutch evangelical Christians are to hold a round-the-clock prayer vigil to ward off the forces of evil on Tuesday - the so-called Devil's Day.
The Devil hates it when we worship God, say organisers
They believe that the sixth day of the sixth month of 2006 has great significance for evil-doers and Satanists who revere the number 666.
In a bid to counteract the forces of evil, more than 2,000 Dutch Christians will hold "a violent day of worship".
They will be joined by Christians in 23 other countries, organisers say.
The reference to 666 is taken from the Biblical book of Revelation, which talks about the events leading to the end of the world.
Revelation 13:18 states: "If anyone has insight, let him calculate the number of the beast, for it is man's number. His number is 666."
Behind the initiative is a Dutch evangelical organisation called Ambassadors Ministries.
Mathijs Piet, one of the organisers, told the BBC news website that the prayer marathon was to officially start at 1800 on Monday with a prayer rally in Jerusalem.
"666 is the number of the Devil and we know that on this date, Satanists will try and do many things, so we Christians try and do the opposite," Mr Piet said.
"We know the Devil hates it when we worship God."
Organisers expect at least 2,000 Dutch evangelicals to take part in the mass prayer vigil across the Netherlands.
They are not the only ones to note the significance of the date.
Film company 20th Century Fox has chosen the same date to launch its remake of the 1976 horror classic The Omen, in which a man comes to realise his son is the Antichrist.
The fear of the number 666 is known as hexakosioihexekontahexaphobia.