Almost 150 Lotto players were just one number away from sharing the €19 million prize in the must-win draw - after picking numbers that appear in a diagonal pattern on the game's playslips.
A total of 149 ticketholders collected a cheque for €36,687 after matching five numbers and the bonus number in the must-be-won game that ended the 62-draw drought.
The Irish Daily Star launched an investigation after it emerged that a higher than average number of players won the Match 5 + Bonus prize in the January 15 draw.
The newspaper's investigative work established these players picked numbers that appear in the specific pattern of a diagonal line on the Lotto playslip.
There were 149 winners of the second highest prize tier - Match 5 + Bonus - on January 15 compared to just 26 winners for this prize tier in the previous 20 draws combined.
An average of 1.3 people win the the Match 5 + Bonus prize in each Lotto draw - but this increased to 149 ticketholders in the will-be-won draw.
The winning numbers for the must-win draw on January 15 were 02, 09, 16, 30, 37, 40 and the bonus was 23.
The numbers 02, 09, 16, 23, 30 and 37 all appear in a diagonal line on the Lotto playslips.
Had the number 44 been picked instead of 40 in the Lotto draw, it's likely that these 149 players would have shared the €19,060,800 prize - and come away with just €127,924.82 each.
A spokesperson for the National Lottery said the large number of players who bought tickets for the must-win draw combined with the number of players who matched a combination of the drawn numbers at this prize tier led to the anomaly.
The spokesperson said: "The special ‘Will be Won’ Lotto draw on January 15 was the first time in the history of the game that Lotto players had the opportunity to play for a guaranteed jackpot prize of €19.06 million, in addition to the guaranteed jackpot prize fund which flowed down to the next winning prize tier.
"The 149 winners of the Match 5 + Bonus prize each won over €36,000, having shared a total prize fund of almost €5.5 million due to the flow-down in prizes because of the €19.06 million jackpot cap.
"The Lotto is a game of chance and therefore the increase in the number of prize winners at these levels was likely due to a number of factors such as the combination of numbers which were drawn on the night and due to the number of players who matched a combination of these numbers at varying prize tiers."
Mathematician Eamonn Toland said Lotto players should not pick their numbers if they want to decrease their chances of having to share the jackpot.
Mr Toland, who is founder of themathstutor.ie, said there is no way a player can increase their odds of winning the Lotto - but players can decrease the odds of having to share a prize if they buy Quick Pick tickets instead of choosing numbers.
He told The Star: "We can literally see what has happened. The players went for a diagonal pattern.
"Visually, it's a diagonal pattern. Or the other way of looking at it is they went up in sevens.
"So they started on 2 and went up in multiples if sevens. Each of those players most likely picked the numbers.
"The 40 number was the only one that came out that they didn't pick in the pattern.
"There was an average of 1.3 people matching the Match 5 + Bonus per draw. So roughly two per week.
"For that to go to 149 is crazy. You could argue that there were more people playing and the people who were playing were buying more lines.
"That probably did happen but not to that extent. Both those factors bump up the likelihood of sharing a prize but for it to go from 1 to 149 is exceptional.
"The pattern is the main thing that caused so many winners.
"The winner's numbers don't have a pattern if you mark them on a playslip.
"They bought a Quick Pick ticket. It's too close to a pattern to be coincidental.
"If someone wanted a pattern, they would just pick the pattern."
Mr Toland, who studied Physics, Maths and Computers in NUI Galway and Queen’s University Belfast before founding an online support system for maths students, said players should buy Quick Pick tickets to avoid playing in patterns.
He said: "People tend to go with patterns but that's a bad idea.
"Ultimately, you want to avoid sharing the jackpot and the way to do that is to avoid patterns.
"To pick randomly, go for Quick Pick and let the machine pick random numbers.
"You could end up with the same numbers as someone else but it's much less likely.
"These players won €36,687 each. If they hadn't done their pattern, they wouldn't have won anything in this draw.
"But in general, it's not a good idea to do a pattern."
The odds of winning the National Lottery jackpot increased from 1 in 8.1 million to 1 in 10.7 million when the number of balls in the draw increased from 45 to 47 in 2015.
Prior to the January 15 draw, nobody had matched all six numbers and the bonus ball since June 5 and the jackpot was capped at € €19,060,800 since October 2.
The must-win mechanism meant that if no ticket holder matched the first six numbers drawn on January 15, the jackpot would have reverted to the next highest prize tier - five numbers and the bonus - and so on until a winner was found.
Irish players will never again see a capped jackpot rolling for months as under new Lotto game rules the jackpot will remain capped for a maximum of five draws.
If there is no outright jackpot winner on the fifth draw at cap, the entire jackpot fund flows down to the next winning prize tier.
And in the future, should the Lotto exceed Saturday night’s jackpot of €19.06m in any given draw, that amount will become the new Lotto jackpot cap.
