isn't the kind of author you'd bump into at lit fests. But his bestselling books have helped many

students lose their dread of

. Sunday Times profiles the tutor turned internet star

He dreams of algorithms that would give most people nightmares. And, spends every waking hour thinking of ways to explain concepts like 'series solution of linear differential equations'. Meet Dr Ravi Dutt Sharma mathematics teacher and author of 25 reference books — whose name evokes as much awe as the subject he teaches. And though students have used his thick tomes for the last 31 years to ace the dreaded maths exam, it's only recently that a spoof video turned the tutor into a YouTube star.The Viral Fever (TVF) video 'A day with R D Sharma' stars an eccentric genius and his obsession with numbers. Sharma, in the video, prays to deity 'X', eats chapatis with a 5cm diameter made painstakingly with a compass, gives directions that involve using a protractor to find the right road and his mobile ringtone is the hit song from Madhuri-starrer Tezaab, 'Ek, do, teen'. India's preoccupation with maths and R D Sharma can be judged by the fact that the video has notched up 3.5 million views.Shown the video by his students, the real-life R D Sharma had a good laugh but said he shared little with his on-screen persona except for the love for maths. "I like to spend all my time thinking and writing about maths problems. I find it relaxing," he says. When he is not writing books explaining mathematical concepts for classes 6 to 12 and engineering students, Sharma is busy dispensing his duty as vice-principal and head of department of science and humanities at Delhi government's Guru Nanak Dev Institute of Technology.The son of a poor Rajasthan farmer who walked 15km to school before his father finally saved up enough to buy him a cycle, Sharma says his love for the subject blossomed early. Lying on a charpoy under the stars, Sharma senior would make his son recite multiplication tables up to 40 before he could go to bed. By age 9, Sharma had not only mastered the tables but also knew the square roots and cube roots of numbers till 20. Not surprisingly, the boy would top his class in the tiny village of Bhoopkhera in Behror tehsil, over 150km from Delhi. Times were tough and Sharma recalls how his father borrowed money to pay for his graduation.He turned author by sheer accident. Sharma was doing his PhD from Rajasthan University when a senior teacher who taught linear algebra passed away. "There was a vacuum because there was no standardised Indian textbook for the subject. The only book that could be used was by a foreign author and very expensive. I had scored 100% in the subject. So I stepped in to write my first book in 1986. It was not only adopted in the university but continued to be used for the next 10-11 years," he says.There was no looking back after that. Reluctant to part with sales figures, Dhanpat Rai Publications owner Ish Kapur claims that Sharma's books are best-selling in the class 9 to 12 segment. Last year 25 lakh students gave the CBSE board exam for classes 10 and 12 and it's reasonable to assume that a significant number used Sharma's books. "If I say that CBSE students from Kashmir to Kanyakumari use Dr Sharma's books, it would not be an exaggeration. We cover 10,000 schools in the country and our books go to West Asia and Singapore, even to the US," Kapur says.Chandan Kumar, who co-wrote the hit TVF video, recalls channelling his Patna school days when everyone was swotting from R D Sharma or R S Aggarwal's books to bring the man to life. "While discussing the script, we realised maths was a subject that inspires strong emotions. People either love or hate it, there is no indifference. So we wrote about a guy whose life revolves around maths," he says. One tortured soul posted how Sharma was way more strict than the video portrayal while many others acknowledged his contribution to their maths results.A student who prepared for his engineering entrance exams in 1999-2000 under Sharma recalls a test where the highest marks were just 25 out of 50. "That was a jolt, and he humiliated us further by saying that he expected a lot more. I remember one of my fellow students saying to me, 'Yeh banda andar aag laga deta hai' (this man motivates me)." A joke this blogger used to crack goes like this: "Let Sharma = X, then R.D. Sharma = R.D.X."Students may be mixed in their reactions but clearly there is no denying the popularity of Sharma's books. Mohammed Azam Khan who runs Azam's Maths Classes in Lucknow describes the teacher's influence with flair. "People are fans of filmstars. For us, he is Amitabh Bachchan."