Sound power: Difference between revisions

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en>Dondervogel 2
m sound power level is measured in decibels (not watts)
en>Dondervogel 2
m →‎Table of selected sound sources: source refers to "steel wheels"; also "city traffic" though mentioned in source does not make sense
 
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A '''centered hexagonal number''', or '''hex number''', is a [[centered polygonal number|centered]] [[figurate number]] that represents a [[hexagon]] with a dot in the center and all other dots surrounding the center dot in a [[hexagonal lattice]].


{|
! 1 !! !! 7 !! !! 19 !! !! 37
|- style="color: red" align="center" valign="middle"
| +1</span> || || +6 || || +12 || || +18


|- align="center" valign="middle"
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|}
 
The {{mvar|n}}th centered hexagonal number is given by the formula
 
:<math>n^3 - (n-1)^3 = 3n(n-1)+1.\,</math>
 
[[Image:Centered hexagonal = 1 + 6triangular.svg|thumb|right]]
Expressing the formula as
 
:<math>1+6\left({1\over 2}n(n-1)\right)</math>
 
shows that the centered hexagonal number for {{mvar|n}} is 1 more than 6 times the {{math|(''n'' − 1)}}th [[triangular number]].
 
The first few centered hexagonal numbers are
 
:[[1 (number)|1]], [[7 (number)|7]], [[19 (number)|19]], [[37 (number)|37]], [[61 (number)|61]], [[91 (number)|91]], [[127 (number)|127]], [[169 (number)|169]], 217, 271, 331, 397, 469, 547, 631, 721, 817, 919.
 
In [[base 10]] one can notice that the hexagonal numbers' rightmost (least significant) digits follow the pattern 1–7–9–7–1.
 
Centered hexagonal numbers have practical applications in materials logistics management, for example, in [[packing problem|packing]] round items into larger round containers, such as [[Vienna sausage]]s into round cans, or combining individual [[wire]] strands into a [[cable]].
 
The sum of the first {{mvar|n}} centered hexagonal numbers happens to be [[cube (algebra)|{{math|''n''<sup>3</sup>}}]]. That is, centered hexagonal [[pyramidal number]]s and [[cubic number|cubes]] are the same numbers, but they represent different shapes.  Viewed from the opposite perspective, centered hexagonal numbers are differences of two consecutive cubes, so that the centered hexagonal numbers are the [[figurate number#Gnomon|gnomon]] of the cubes. In particular, [[prime number|prime]] centered hexagonal numbers are [[cuban prime]]s.
 
The difference between {{math|(2''n'')<sup>2</sup>}} and the {{mvar|n}}th centered hexagonal number is a number of the form {{math|3''n''<sup>2</sup> + 3''n'' − 1}}, while the difference between {{math|(2''n'' − 1)<sup>2</sup>}} and the {{mvar|n}}th centered hexagonal number is a [[pronic number]].
 
==See also==
*[[Hexagonal number]]
*[[Flower of Life]] (generated by circles arranged in a centered hexagonal pattern)
*[[Magic hexagon]]
*[[Star number]]
 
{{Classes of natural numbers}}
 
{{DEFAULTSORT:Centered Hexagonal Number}}
[[Category:Figurate numbers]]

Latest revision as of 16:27, 28 December 2014


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