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0|0|0|||||digits sum|xordan|1|20:35:48|06/27/2007|Hello%3A    %0D%0AI have found that if two numbers A and B sum C %28A%2BB%3DC%29%2C the sum of the digits of A %2B the sum of the digits of B is similar to the sum of the digits of C. %28reduced to a digit%29    %0D%0ADoes this property have a demonstrable foundation as theorem%3F    %0D%0AIt is alone a curiosity that has arisen when I play with numbers in search of finding a easy test of primality. %0D%0AInvestigating this property I found your site that I find very interesting and informative and it contains similar topics  those that I ask. %0D%0A   %0D%0AThank you for your time and attention. %0D%0A%0D%0Axordan.tom%40gmail.com%0D%0A%0D%0AP.S.%3A Original in spanish
1|1|0|||||RE%3A digits sum|alexb||01:37:13|07/04/2007|%3EHello%3A %0D%0A%3EI have found that if two numbers A and B sum C %28A%2BB%3DC%29%2C the %0D%0A%3Esum of the digits of A %2B the sum of the digits of B is %0D%0A%3Esimilar to the sum of the digits of C. %28reduced to a digit%29 %0D%0A%0D%0AThe sum of the digits %28reduced to a single digit%29 is known as %5Bem%5Ddigital root%5B%2Fem%5D. This has the property%2C indeed%2C that the digital root of the sum equals to the %28reduced if necessary%29 sum of digital roots. The same holds for products.%0D%0A%0D%0AThe digital root of a number divisible by 9 is 9. Otherwise%2C the digital root of a number N is N %28mod 9%29.%0D%0A%0D%0A