Properties of the Number -81

Eighty-One

Basics

Value: -82 → -81 → -80

Parity: odd

Prime: No

Previous Prime:

Next Prime: 1

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: No

Catalan Number: No

Vampire Number: No

Taxicab Number: No

Super Prime: No

Friedman Number: No

Fermat Number: No

Cullen Number: No

OEIS Sequences

Triangle read by rows. T(n, m) are the coefficients of Sidi polynomials. A75513

Scaled Chebyshev U-polynomials evaluated at sqrt(3)/2; expansion of 1/(1 - 3·x + 3·x²). A57083

Triangle read by rows: coefficients T(n,k) of a binomial decomposition of 2ⁿ-1 as Sum(k=0..n)T(n,k)*binomial(n,k). A244124

a(n) = 3·a(n-2) - a(n-3) with a(0)=0, a(1)=3, a(2)=0. A214699

a(n) = ∑_{j=0..floor(n/3)} (-1)^j*binomial(n,3·j+1). A57682

Alternating sum of cubes, i.e., ∑_k=0..n k^p*q^k for p=3, q=-1. A232599

Triangle of coefficients in expansion of (x-1)*(x-3)*(x-5)*...*(x-(2·n-1)). A39757

Dirichlet inverse of the gcd-sum function (A018804). A101035

Determinant of the n X n matrix whose element (i,j) equals the |i-j|-th prime or if i=j, 1. A71078

Irregular triangle read by rows: mean version of Girard-Waring formula A210258, for m = 3 data values. A287768