1 > heero 'reference for leader of the gundam pilots'
2 > duo 'means two in italian (i think)
3 > trowa 'trois = three in french'
4 > quatre 'means four in french'
5 > wufei 'if you say this name, you can hear five somehow'
6 > zechs 'means six in german'
13 > treize 'means thirteen in french'
the most common pairings are 1x2, 1x2x5, 3x4, 6x13, 13x5