Properties of the Number 81

Eighty-One

Basics

Value: 80 → 81 → 82

Parity: odd

Prime: No

Previous Prime: 79

Next Prime: 83

Digit Sum: 9

Digital Root: 9

Palindrome: No

Factorization: 3 ⁴

Divisors: 1, 3, 9, 27, 81

Polygonal

Triangular: No

Square: Yes

Pentagonal: No

Hexagonal: No

Heptagonal: Yes

Tetrahedral: No

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Representations

Binary: 1010001

Octal: 121

Duodecimal: 69

Hexadecimal: 51

Square: 6561

Square Root: 9

Classification

Fibonacci: No

Bell Number: No

Factorial Number: No

Regular Number: Yes

Perfect Number: No

Special

Kaprekar Constant: No

Munchausen Constant: No

Armstrong Number: No

Kaprekar Number: Yes

Catalan Number: No

Vampire Number: No

Taxicab Number: No

Super Prime: No

Friedman Number: No

Fermat Number: No

Cullen Number: No

OEIS Sequences

Coordination sequence for planar net 3.3.3.3.6 (also called the fsz net). A250120

The squares: a(n) = n². A290

The odd numbers: a(n) = 2·n + 1. A5408

Powers of primes. Alternatively, 1 and the prime powers (p^k, p prime, k >= 1). A961

a(n) = n' = arithmetic derivative of n: a(0) = a(1) = 0, a(prime) = 1, a(m·n) = m·a(n) + n·a(m). A3415

The composite numbers: numbers n of the form x·y for x > 1 and y > 1. A2808

Completely multiplicative with a(prime(k)) = prime(k+1). A3961

Powers of 3: a(n) = 3ⁿ. A244

Perfect powers: m^k where m > 0 and k >= 2. A1597

Numbers that are not squarefree. Numbers that are divisible by a square greater than 1. The complement of A005117. A13929

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