Names of 81991
| Nominal | 81991 |
| Cardinal | eighty-one thousand nine hundred ninety-one |
| Ordinal | 81,991st |
| This number as US currency | eighty-one thousand nine hundred ninety-one dollars |
| Is 81991 an odd number? | 81991 is an odd number |
| Is 81991 an even number? | 81991 is NOT an even number |
| Is 81991 a palindrome? | 81991 is NOT a palindrome number |
| Is 81991 a triangle number? | 81991 is NOT a triangle number |
81991 in other Bases
| Base 2 (Binary) | 101000000010001112 |
| Base 3 (Ternary) | 110111102013 |
| Base 4 (Quaternary) | 1100010134 |
| Base 5 (Quinary) | 101104315 |
| Base 6 (Senary) | 14313316 |
| Base 8 (Octal) | 2401078 |
| Base 12 (Duodecimal) | 3B54712 |
| Base 16 (Hexadecimal) | 1404716 |
| Base 20 (Vigesimal) | A4JB20 |
Primes and Factors tests for 81991
| Is 81991 a Prime Number? | 81991 is NOT a prime |
| Is 81991 a perfect number? | 81991 is NOT a perfect number |
| Is 81991 a Mersenne Prime? | 81991 is NOT a Mersenne prime |
| Is 81991 a Fermat Prime? | 81991 is NOT a Fermat prime |
| Is 81991 a Fibonacci Prime? | 81991 is NOT a Fibonacci prime |
| Is 81991 a Partition Prime? | 81991 is NOT a Partition prime |
| Is 81991 a Pell Prime? | 81991 is NOT a Pell prime |
| Prime Factors | Prime factors of 81991 |
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81991 in other Numerals
| 81991 in Roman Numeral | LXXXMCMXCI |
| 81991 in Chinese Numeral | 捌萬壹仟玖佰玖拾壹 |
| 81991 in Egyptian Numeral | 𓂴𓆼𓍪𓎎𓏺 |
| 81991 in Babylonian Numeral |    |
Roots and stuff for 81991
| Is 81991 a square number? | 81991 is NOT a square number |
| Is 81991 a cube number? | 81991 is NOT a cube number |
| Square root of the number 81991 | 286.34070615265 |
| Cube root of the number 81991 | 43.443225355086 |
Recreational math for 81991
| Number 81991 reversed | 19918 |
| Sum of the digits | 28 |
| No of digits | 5 |