Job ad that challenged readers to solve a maths puzzle backfires The Australian Air Force posted a job advert looking for a engineer New recruits were told to solve a complicated maths puzzle to get the phone number needed to apply - yet the puzzle proved to be insolvable The typos were spotted by Reddit users and formula has been corrected It was a job advert designed to find the best mathematical minds in the country by hiding a phone number inside a complicated numerical puzzle. But the Royal Australian Air Force, which posted the ad, has been left red-faced after failing to spot a mistake in the numbers, therefore making the puzzle insolvable. The typos were eventually spotted by users of the website Reddit and the formula has now been corrected. A job advert for an engineer at the Royal Australian Air Force was meant to hide its recruitment phone number inside a maths puzzle. The first four terms shown in the formula added together give this number but the final terms should have then equaled zero. The two typos, highlighted, made the task impossible According to Business Insider Australia (BIA), the Defence Force recruiters got the formula from a University of Melbourne professor. The Force told the website that the formula was designed as a 'means of driving engagement, and not a formal test.' The site said: 'That's good, because the formula - which involves infinite sums, integrals, complicated trigonometry and imaginary numbers - doesn't produce the intended phone number.' Reddit users solved the first four terms shown in the formula and added them together to get the Defence Jobs phone number of 131901. Defence Force Recruiting has since corrected the formula on its website, pictured, by replacing sin 2 x with sin (2x) in the third to last line, and (2k-1)! with (2k+1)! in the penultimate line. The Force thanked the Reddit members who spotted the mistake, adding: 'you are exactly the kind of people we'd be looking for' However, they discovered that the remaining terms were meant to equate to zero but two typos in the formula made this impossible. The incorrect formula showed 'sin to the power of two x' when it should have read sin (2x). To get zero in the penultimate line the formula should have said (2k+1)! instead of (2k-1)! Defence Force Recruiting has since corrected the formula and told BIA: 'Our original formula included two small typos, which we have now fixed. We hope people still enjoy the inherent fun and hidden challenges. 'Our thanks go to the eagle-eyed Reddit users who spotted them first; you are exactly the kind of people we'd be looking for.'