Properties of the Number 21681

Twenty-One Thousand Six Hundred Eighty-One

Basics

Value: 21680 → 21681 → 21682

Parity: odd

Prime: No

Previous Prime: 21673

Next Prime: 21683

Digit Sum: 18

Digital Root: 9

Palindrome: No

Factorization: 3 ³ × 11 × 73

Divisors: 1, 3, 9, 11, 27, 33, 73, 99, 219, 297

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

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Representations

Binary: 101010010110001

Octal: 52261

Duodecimal: 10669

Hexadecimal: 54b1

Square: 470065761

Square Root: 147.2446943016963

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 of coefficients of g.f. a*(1+x)ⁿ + b*(1-x)ⁿ⁺²*polylog(-n-1, x)/x + 2ⁿ*c*(1-x)ⁿ⁺¹*LerchPhi(x, -n, 1/2), with a = -2, b = 2, c = 1. A168524

a(0) = a(1) = 1; a(n) = 3 * ∑_k=0..n-2 a(k) * a(n-k-2). A354734

Denominators of continued fraction convergents to sqrt(876). A42693

Denominators of continued fraction convergents to sqrt(977). A42891

a(n) = n*(2·n² + 5·n + 13)/2. A163655

Nonnegative values·of solutions (x, y) to the Diophantine equation x² + (x+511)² = y². A207078

Numerators of rational coefficients which are ratio of Brent's coefficients -A[n,2]/A343480. A380947

Number of n X n binary arrays symmetric under horizontal reflection with all ones connected only in a 11100-00100-00111 pattern in any orientation. A147248

Central trinomial coefficients: largest coefficient of (1 + x + x²)ⁿ. A2426

Number of ways to place 5 nonattacking zebras on an n X n board. A172140