India's digital payments unicorn Paytm, backed by Chinese business magnate Jack Ma's Ant Group, Japan's Softbank and US investor Warren Buffett-owned Berkshire Hathaway, launched the country's biggest-ever initial public offering (IPO) Monday.

Paytm, founded by India's youngest dollar billionaire Vijay Shekhar Sharma in 2010, aims to raise close to USD 2.5 billion via the IPO. And if fully subscribed, the IPO would make Paytm's valuation at USD 20 billion.

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According to figures released by the Securities and Exchange Board of India (SEBI), on the first day, the IPO was 

subscribed 18% -- which included 73% of the portion set aside for retail investors. The IPO ends Wednesday.

Sharma, the man behind Paytm, is a self-made businessman. Till the age of 15, he had no English skills and he learnt the language by listening to rock music.

"That sort of gave me an underdog-ish feeling. And I think that over the period, I have championed underdog-ism. And I feel that I want to be the best underdog story out of India," Sharma, now in his early 40s, said during an interview three years ago.

Paytm's IPO comes barely three and a months after India's food delivery giant Zomato became the country's first new-age technology unicorn to list on the bourses.

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Zomato's listing price was Rs 115 and Rs 116 on the Bombay Stock Exchange and the National Stock Exchange (NSE), respectively, as against the offer price of Rs 76. NSE's flagship NIFTY 50 index is used by domestic and global investors as a barometer of the Indian capital markets.