21 (twenty-one) is the natural number following 20 and preceding 22.

Twenty-one is the fifth discrete Semiprime and the second in the (3.q) family. With 22 it forms the second discrete Semiprime pair. As it is a semiprime with both its prime factors being Gaussian primes, 21 is then a Blum integer.

Twenty-one is a Fibonacci number, a Harshad number, a Motzkin number, a triangular number and an octagonal number, as well as a composite number, its proper divisors being 1, 3 and 7.

21 is the sum of the first six natural numbers (1+2+3+4+5+6=21).

21 has an aliquot sum of 11 though it is the second composite number found in the 11-aliquot tree with the abundant square prime 18 being the first such member. Twenty-one is the first number to be the aliquot sum of three numbers 18, 51, 91.

21 appears in the Padovan sequence, preceded by the terms 9, 12, 16 (it is the sum of the first two of these).

The sum of divisors for the integers 1 through 6 is 21.

21 is a repdigit in base 4 (111).

21 is the smallest natural number that is not close to a power of 2, 2^n, where the range of closeness is +- n.

Maharana Pratap or Pratap Singh (May 24, 1540 – January 19, 1597) was a Hindu ruler of Mewar, a small region in north-western India in the present day state of Rajasthan. In popular Indian culture, Pratap is considered to exemplify the qualities like bravery and chivalry to which Rajputs aspire, especially in context of his opposition to the Akbar. The struggle between Rajput confederacy led by Pratap Singh, and the Mughal Empire under Akbar, has often been characterised in popular Hindutva culture as a struggle between Hindus and the 'invading' Muslims, much on the same lines as the struggle between Shivaji and Aurangzeb a little less than a century later. However, notably, unlike Shivaji, Pratap Singh has also symbolised the pride and prestige of upper caste Hindus in northern India, because of the obvious differences between their lineages - but this allegation have little truth because much of Pratap's own soldiery were recruited from among tribal people like Bhils and backward castes like Lohars, while his own upper caste contemporaries like Man Singh of Amber supported Mughals.

Tarak Mehta (born 1930) is an Indian columnist, humorist, writer and playwright. best known for the column Duniya Na Undha Chasma in Gujarati Language. He has translated and adapted several comedies into Gujarati, and has been well-known figure in the Gujarati theatre.

The humorous weekly column first appeared in Chitralekha in March 1971 and ever since has been looking at contemporary issues from a different perspective. He has published 80 books, over the years, three books are based on the columns he wrote in Gujarati newspaper, Divya Bhaskar while rest were compiled from the stories in Taarak Mehta Ka Ooltah Chashmah.

In 2008 SAB TV, a popular entertainment channel in India, started a show Taarak Mehta Ka Ooltah Chashmah that is based on his column., and soon it became the flagship show of the channel.

He stays in Ahmedabad, Gujarat, where he moved in year 2000, with second wife, Indu of over 30 years, His first wife, Ila who later married Manohar Doshi, (died 2006), also stayed in the same apartment building. He has daughter from his first marriage, Ishani, who stays in US, and has two children, Kushan and Shaili.

Jeremy Kyle (born 7 July 1965) is an English radio and television presenter, best known for his British daytime television chat show on ITV, The Jeremy Kyle Show. Kyle is also the host of an American talk show of the same name which premiered on 19 September 2011.

From 1986-95, Kyle worked as a salesman for life insurance, recruitment, and radio advertising. He then became a radio presenter and after a brief stint at Orchard FM in Taunton and Leicester Sound in Leicester, he was signed by Kent's Invicta FM in 1996. In 1997, he joined BRMB in Birmingham, presenting the shows Late & Live and Jezza's Jukebox.

In 2000, Kyle moved to the Century FM network, taking this format with him. The show was called Jezza's Confessions. It was broadcast between 9pm and 1am. He won a Sony Award for Late & Live in 2001. On 1 July 2002, he made his first broadcast on Virgin Radio, presenting Jezza's Virgin Confessions every weekday from 8pm to midnight. In mid-2003, he broadcast the show from 9pm to 1am every weekday, and in January 2004 the show went out from 10pm to 1am, Sunday to Thursday. He left Virgin Radio in June 2004. From 5 September 2004, Kyle presented the Confessions show on London's Capital FM. The new programme aired Sunday to Thursday from 10pm to 1am with live calls on relationship issues of all kinds. Capital Confessions came to an end on 22 December 2005 to make way for The Jeremy Kyle Show, a similar show which ran from January 2006 to December 2006.

Demetria Devonne "Demi" Lovato (born August 20, 1992) is an American singer-songwriter, musician, and actress. Her earliest roles included Angela on Barney & Friends, before she became better known for her starring roles in the Camp Rock movies, as Sonny Munroe in the Disney sitcom Sonny with a Chance, and as the star of the 2009 movie Princess Protection Program. She is also involved in philanthropic activities through charity work and various social and environmental causes.

As a solo musical artist, Lovato released her debut album Don't Forget on September 23, 2008. The album debuted at number two on the Billboard 200 selling 89,000 copies in the first week. It has since shipped over 500,000 copies, earning a gold certification in the United States. Lovato released her second album, Here We Go Again, on July 21, 2009. The album debuted at number one on the Billboard 200, selling 108,000 copies in the first week. Her third studio album, Unbroken, was released on September 20, 2011 and peaked at number four on the Billboard 200. She is working on her fourth studio album.