Properties of the Number 20805

Twenty Thousand Eight Hundred Five

Basics

Value: 20804 → 20805 → 20806

Parity: odd

Prime: No

Previous Prime: 20789

Next Prime: 20807

Digit Sum: 15

Digital Root: 6

Palindrome: No

Factorization: 3 × 5 × 19 × 73

Divisors: 1, 3, 5, 15, 19, 57, 73, 95, 219, 285

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

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Representations

Binary: 101000101000101

Octal: 50505

Duodecimal: 10059

Hexadecimal: 5145

Square: 432848025

Square Root: 144.23938435808716

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 a(0) = a(1) = 1, and n·a(n) = 2*(-7+5·n)*a(n-1) + 9*(2-n)*a(n-2) for n >= 2. A162326

Palindromic numbers in bases 2 and 8 written in base 10. A259380

Palindromic numbers in bases 4 and 8 written in base 10. A259382

Array read by antidiagonals: T(n,k) is the number of graphs on n labeled nodes, each node being colored with one of k colors, where no edge connects two nodes of the same color. A322280

G.f. A(x,y) satisfies: x·y = ∑_n=-oo..+oo (-1)ⁿ * x^n*(n+1/2) * A(x,y)ⁿ, with coefficients T(n,k) of xⁿ*y^k in A(x,y) given as a triangle read by rows. A355350

-3-Knödel numbers. A225507

Numbers n palindromic in exactly three bases b, 2 <= b <= 10. A214425

T(n,k)=Number of nXk 0..1 arrays with every element unequal to 0, 1, 2, 3, 5, 6, 7 or 8 king-move adjacent elements, with upper left element zero. A317604

Expansion of 1/(1+x+2·x²-x³). A77978

Positive numbers such that both their binary and negabinary representations are palindromic. A331894