Properties of the Number 21840

Twenty-One Thousand Eight Hundred Forty

Basics

Value: 21839 → 21840 → 21841

Parity: even

Prime: No

Previous Prime: 21839

Next Prime: 21841

Digit Sum: 15

Digital Root: 6

Palindrome: No

Factorization: 2 ⁴ × 3 × 5 × 7 × 13

Divisors: 1, 2, 3, 4, 5, 6, 7, 8, 10, 12

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

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Representations

Binary: 101010101010000

Octal: 52520

Duodecimal: 10780

Hexadecimal: 5550

Square: 476985600

Square Root: 147.78362561528934

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

Triangle read by rows. A generalization of unsigned Lah numbers, called L[4,1]. A48854

Numbers n that raised to the powers from 1 to k (with k>=1) are multiple of the sum of their digits (n raised to k+1 must not be a multiple). Case k=10. A135195

a(n) = n*(n + 1)*(n + 2)*(n + 3)/2. A33486

A partition product of Stirling₂ type [parameter k = -4] with biggest-part statistic (triangle read by rows). A157398

Triangle read by rows: T(n,k) = number of open trails of length k starting and ending at fixed distinct vertices in the complete undirected graph on n labeled vertices, for n >= 1 and k = 0 .. n*(n-1)/2. A357886

Numbers k such that k-1, k+1 and k²+1 are prime numbers. A70155

If X₁,...,X_n is a partition of a 2n-set X into 2-blocks then a(n) is equal to the number of 4-subsets of X containing none of X_i, (i=1,...,n). A130810

a(n) = 20·a(n-1) - 64·a(n-2) for n > 1; a(0) = 85, a(1) = 1364. A166917

Numbers n such that the multiplicative group modulo n is the direct product of 6 cyclic groups. A272596

Triangle read by rows: T(n,k) is the numerator of R(n,k) defined implicitly by the identity ∑_i=0..l-1 ∑_j=0..m R(m,j)*(l-i)^j*i^j = l^2·m+1 holding for all l,m >= 0. A302971