The Number 81
81 is a Heptagonal Number.
81 is a 28-gonal Number.
81 is a Centered Octagonal Number.
The 81 stable Chemical Elements.
The Chemical Element Thallium has an atomic number of 81.
The 81 permutations of yin, yang and tao over 4 places.
Of the 117 scales of Chinese Dragons 81 are yang and benevolent.
The Year 81 ADIn the year 81 AD The Arch of Titus was constructed.