Thousands of yrs passed,Millions of theorems derived,Crores of formulas made, But still..."x" is unknown&..."xxx" is well known!!
When mathematician Ramanujan (1887-1920) was asked 'How friends should be?', his reply was: 'They should be like the numbers 220 and 284!'
The proper divisors of 220 are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55 and 110, of which the sum is 284
The proper divisors of 284 are 1, 2, 4, 71 and 142, of which the sum is 220
220 & 284 are known as 'amicable numbers' in the world of mathematics!