The seven planets known to the Romans included the sun and the moon, revolved around the earth, were named after gods, and gave us our seven days in a week. There are seven continents, seven seas, and on the way the Saint Ives I met a man with seven wives. Seven is either a lucky number or an unlucky number. It’s not very divisible. In three-dimensional space, the seven crystal systems, are not commonly appreciated.

seven • sieben • zeven • sept • sju • syv • sjö • sedm • siedem • sette • siete • yedi • seitse • sebati • saat