Properties of the Number 20991

Twenty Thousand Nine Hundred Ninety-One

Basics

Value: 20990 → 20991 → 20992

Parity: odd

Prime: No

Previous Prime: 20983

Next Prime: 21001

Digit Sum: 21

Digital Root: 3

Palindrome: No

Factorization: 3 × 6997

Divisors: 1, 3, 6997, 20991

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

Today's Target

2196 Try Today's Challenge

Representations

Binary: 101000111111111

Octal: 50777

Duodecimal: 10193

Hexadecimal: 51ff

Square: 440622081

Square Root: 144.88271118390904

Classification

Fibonacci: No

Bell Number: No

Factorial Number: No

Regular Number: No

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

List of different composites in Pascal-like triangles with index of asymmetry y = 3 and index of obliqueness z = 0 or z = 1. A141069

A sequence of asymptotic density ζ(10) - 1, where ζ is the Riemann ζ function. A143036

Sum of the areas of all bargraphs of site-perimeter n. A274208

Numbers k such that the continued fraction for sqrt(k) has even period and if the last term of the periodic part is deleted the central term is 96. A31594

Records in the sequence A024573 defined by [1/{n·e}], {x} := x - [x]. A101262

Largest value of k for which Golay-Rudin-Shapiro sequence A020986(k) = n. A20991

a(n) = start of a sequence of at least n consecutive primes, p₁, p₂, ..., p_n (say), all == 1 mod 4, such that A(p₁) > A(p₂) > ... > A(p_n), where A(p) (see A145010) is the area of the Pythagorean triangle with hypotenuse p. A144954