Properties of the Number 21820

Twenty-One Thousand Eight Hundred Twenty

Basics

Value: 21819 → 21820 → 21821

Parity: even

Prime: No

Previous Prime: 21817

Next Prime: 21821

Digit Sum: 13

Digital Root: 4

Palindrome: No

Factorization: 2 ² × 5 × 1091

Divisors: 1, 2, 4, 5, 10, 20, 1091, 2182, 4364, 5455

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

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Representations

Binary: 101010100111100

Octal: 52474

Duodecimal: 10764

Hexadecimal: 553c

Square: 476112400

Square Root: 147.71594362153328

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

E.g.f.: exp(x + 3/2·x²). A115327

Triangle read by rows: T(n,k) is the number of subpermutations of an n-set whose orbits are each of size at most k, and without fixed points. Equivalently, T(n,k) is the number of partial derangements of an n-set each of whose orbits is of size at most k. A261762

Values of k such that the total number of 1's in the binary expansions of the first k integers is a multiple of k. A95376

Number of basis partitions of n+81 with Durfee square size 9. A69252

Number of partitions of n into colored blocks of equal parts, such that all colors from a set of size six are used and the colors are introduced in increasing order. A327289

a(0) = 1, a(1) = 0, a(2) = 1; a(n) = a(n-1) + ∑_k=0..n-3 a(k) * a(n-k-3). A357307

a(n) = 25·n²/2 - 11·n/2 + 1. A383465

Triangle read by rows: T(n,k) is the number of length n left factors of Dyck paths having k DUU's, where U=(1,1) and D=(1,-1). A191795

Number of isomorphism classes k of groups G of order p·2ⁿ when G contains a unique Sylow p subgroup and the maximal 2^m dividing p-1 is such that 2^m >= 2ⁿ. A376349

a(n) is the coefficient of xⁿ/n! in exp(x + n·x²/2). A277614