Every number is associated with something sacred and has sacredness to it. That’s why when the Rudrabhishekam is done, all the numbers are said.
Number 1 and 2 are very sacred. Number 3 is also sacred. Number 3 is associated with so many things, Brahma, Vishnu and Mahesh; satva, rajas and tamas; vata, pitta and kapha; morning, afternoon and evening; present, past and future. So number 3 is very sacred.
Then number 4 is more sacred. The four directions; the four Vedas has so much sacredness attached to it. The most sacred of the symbols, Swastika, has four corners.
Then number 5, the five elements which are very sacred; the five organs of senses; five organs of perceptions; five organs of action. Pancha Devata, there are five important categories of Devatas. A village panchayat has only five members and so 5 is very sacred.
Then comes 6, Shad Darshanas, the six systems of Hindu philosophy; Shadangas, the six angas are very important. Then the sixth sense, you say the mind is the sixth sense.
Then 7; seven swaras, seven chakras, seven days of the week, seven planets.
8 has its own sacredness, Ashta Dikpalakas, are the eight divine entities ruling eight quarters or the universe, Ashtadhatu, eight metals which are very essential for the body. Ashtalakshmi, the eight types of wealth. So 8 has its own significance.
Coming to 9, Navagrahas; Navaratna, nine gems; Navaratri, nine nights. In nine months a child is born. There are nine types of bhakti.
10 and 11 is also sacred. No number is left which is not sacred. In the West number 13 is considered unholy, but in India no number is considered unholy or unlucky. All the numbers are good numbers. Every number has some significance, some glory attached to it.