tetrahedral number or trigonometric pyramidal number is the number that can be arranged as a trigonometric pyramidal base. The tetrahedron number is a trigonometric number for each layer, and its formulas are the sum of the first n trigonometric numbers, that is, n(n + 1)(n + 2) / 6. The first few items are: 1, 4, 10, 20, 35, 56, 84, 120... (OEIS:A000292)

The

tetrahedral number parity arrangement is "parity parity".

In 1878, A.J. Meyl proved that only three tetrahedral numbers are square numbers at the same time: 1, 4, 19600. The only number that is both a tetrahedron and a tetragonal cone is 1 (Beukers(1988)).

They can be found in Yang Hui trigonometric every row from right to left or left to right item 4.

formulas

number or trigonometric cone number (T_n) = (n × (n+1) × (n+2)) / 6