A number n is triangular if n == 1 + 2 +…+j for some j.
![A number n is triangular if n == 1 + 2 +…+j for some j.](http://www.huamaodashu.com/wp-content/themes/zimeiti-2/thumb.php?src=http://www.huamaodashu.com/wp-content/themes/zimeiti-2/assets/img/default.png&w=280&h=180)
1. A number n is triangular if n == 1 + 2 +…+j fo…
A number n is vesuvian if it is the sum of two different pairs of squares
![A number n is vesuvian if it is the sum of two different pairs of squares](http://www.huamaodashu.com/wp-content/themes/zimeiti-2/thumb.php?src=http://www.huamaodashu.com/wp-content/themes/zimeiti-2/assets/img/default.png&w=280&h=180)
A number n is vesuvian if it is the sum of two differen…
1. A number n is triangular if n == 1 + 2 +…+j fo…
A number n is vesuvian if it is the sum of two differen…