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# 84 (number)

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 Title: 84 (number) Author: World Heritage Encyclopedia Language: English Subject: Collection: Integers Publisher: World Heritage Encyclopedia Publication Date:

### 84 (number)

 ← 83 84 85 →
Cardinal eighty-four
Ordinal 84th
(eighty-fourth)
Factorization 22× 3 × 7
Divisors 1, 2, 3, 4, 6, 7, 12, 14, 21, 28, 42, 84
Roman numeral LXXXIV
Binary 10101002
Ternary 100103
Quaternary 11104
Quinary 3145
Senary 2206
Octal 1248
Duodecimal 7012
Vigesimal 4420
Base 36 2C36

84 (eighty-four) is the natural number following 83 and preceding 85.

## Contents

• In mathematics 1
• In astronomy 2
• In other fields 3
• References 5

## In mathematics

A hepteract is a seven-dimensional hypercube with 84 penteract 5-faces

84 is the sum of the first seven triangular numbers (making it a tetrahedral number), as well as the sum of a twin prime (41 + 43). Being thrice a perfect number, 84 is itself a semiperfect number.

84 is the lim sup of the largest finite subgroup of the mapping class group of a genus g surface divided by g.

A hepteract is a seven-dimensional hypercube with 84 penteract 5-faces.

## In other fields

Eighty-four is also:

## References

1. ^ http://eclipse.gsfc.nasa.gov/SEsaros/SEsaros084.html
2. ^ http://eclipse.gsfc.nasa.gov/LEsaros/LEsaros084.html
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