Properties of the Number 21685

Twenty-One Thousand Six Hundred Eighty-Five

Basics

Value: 21684 → 21685 → 21686

Parity: odd

Prime: No

Previous Prime: 21683

Next Prime: 21701

Digit Sum: 22

Digital Root: 4

Palindrome: No

Factorization: 5 × 4337

Divisors: 1, 5, 4337, 21685

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

Today's Target

2196 Try Today's Challenge

Representations

Binary: 101010010110101

Octal: 52265

Duodecimal: 10671

Hexadecimal: 54b5

Square: 470239225

Square Root: 147.2582765076381

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

Minimal positive solution·of Pell equation y² - A077426(n)*x² = -4. A78357

Numerators of continued fraction convergents to sqrt(767). A42478

Floor[n(n-1)(n-2)(n-3)/14]. A11924

Denominators of continued fraction convergents to sqrt(421). A41801

Numerators of continued fraction convergents to sqrt(610). A42170

Main diagonal of square table A086623 of coefficients of f(x,y) that satisfies f(x,y) = (1-xy)/[(1-x)(1-y)] + xy·f(x,y)². A86624

a(n) = ∑_k=0..n C(n-k, floor(k/2))*3^k. A97335

G.f. A(x) satisfies: A(x) = x + x² * exp( ∑_k>=1 (-1)^k+1 * A(x^k)² / k ). A363386

Twice the coefficient of sqrt(q) in e^h, where e is the fundamental unit and h is the class number of Q(sqrt(q)), q prime and congruent to 1 mod 4. (The coefficient lies in (1/2)Z, so twice it is an integer.) A225432

Irregular triangle of numerators of the average value of the first letter over all derangements of {1, 2, ..., n} with k descents. A332009