Properties of the Number 21805

Twenty-One Thousand Eight Hundred Five

Basics

Value: 21804 → 21805 → 21806

Parity: odd

Prime: No

Previous Prime: 21803

Next Prime: 21817

Digit Sum: 16

Digital Root: 7

Palindrome: No

Factorization: 5 × 7 ² × 89

Divisors: 1, 5, 7, 35, 49, 89, 245, 445, 623, 3115

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

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Representations

Binary: 101010100101101

Octal: 52455

Duodecimal: 10751

Hexadecimal: 552d

Square: 475458025

Square Root: 147.6651617681029

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

Let p = n-th prime == 3 mod 8; a(n) = sum of quadratic residues mod p that are < p/2. A282721

Expansion of 1/((1-8·x)*(1-10·x)*(1-11·x)*(1-12·x)). A16093

Number of orbits of length n under the map whose periodic points are counted by A001642. A60167

Number of partitions of n such that m(greatest part) = m(1), where m = multiplicity. A240078

Smallest m such that A065623(m) = n. A65624

Number of minimal edge covers in the n-trapezohedral graph. A379550

Number of n X n binary arrays symmetric under horizontal and vertical reflection with all ones connected only in a 11011-01110 pattern in any orientation. A147225

Composite numbers coprime to 6 such that A179382(n) = A000265(n-1), the odd part of n-1. A225913

Number of singular vector tuples for a general n X n X n tensor. A271905

First terms "a" of quadruples a>b>c>d>0 with six square pairwise sums. A175534