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Octahedral number : ウィキペディア英語版
Octahedral number

In number theory, an octahedral number is a figurate number that represents the number of spheres in an octahedron formed from close-packed spheres. The ''n''th octahedral number O_n can be obtained by the formula:〔.〕
:O_n=.
The first few octahedral numbers are:
:1, 6, 19, 44, 85, 146, 231, 344, 489, 670, 891 .
==Properties and applications==
The octahedral numbers have a generating function
: \frac = \sum_^ O_n z^n = z +6z^2 + 19z^3 + \cdots .
Sir Frederick Pollock conjectured in 1850 that every number is the sum of at most 7 octahedral numbers: see Pollock octahedral numbers conjecture.〔.〕
In chemistry, octahedral numbers may be used to describe the numbers of atoms in octahedral clusters; in this context they are called magic numbers.〔.〕〔.〕

抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)
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