if there are two payments a year, at the beginning of the year and at 6 months, plus one payment at the end of 21 months then at an annualised compound rate of 21.9% your money will double in 21 months.
(21-21)+(21-21)+21 = 0+0+21 = 21
The LCM is 21.
21
That would be the Guinea, it was a gold coin and was equal to 21 shillings in the British pre-decimal system.
On the Money - 2005 2013-09-21 was released on: USA: 21 September 2013
On the Money - 2005 2013-12-21 was released on: USA: 21 December 2013
Fast Money - 2007 2011-07-21 was released on: USA: 21 July 2011
Fast Money - 2007 2011-09-21 was released on: USA: 21 September 2011
Fast Money - 2007 2011-11-21 was released on: USA: 21 November 2011
Fast Money - 2007 2011-12-21 was released on: USA: 21 December 2011
Fast Money - 2007 2011-04-21 was released on: USA: 21 April 2011
Fast Money - 2007 2011-06-21 was released on: USA: 21 June 2011
Fast Money - 2007 2013-01-21 was released on: USA: 21 January 2013
Fast Money - 2007 2013-02-21 was released on: USA: 21 February 2013
Fast Money - 2007 2013-03-21 was released on: USA: 21 March 2013
Fast Money - 2007 2013-05-21 was released on: USA: 21 May 2013