Properties of the Number 21691

Twenty-One Thousand Six Hundred Ninety-One

Basics

Value: 21690 → 21691 → 21692

Parity: odd

Prime: No

Previous Prime: 21683

Next Prime: 21701

Digit Sum: 19

Digital Root: 1

Palindrome: No

Factorization: 109 × 199

Divisors: 1, 109, 199, 21691

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

Today's Target

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Representations

Binary: 101010010111011

Octal: 52273

Duodecimal: 10677

Hexadecimal: 54bb

Square: 470499481

Square Root: 147.27864746798838

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

a(0) = 1; for n > 0, a(n) = 41·n² + 2. A206399

Expansion of 1/(1 - x² - x⁷ - x¹² + x¹⁴) (a Salem polynomial). A143619

a(n) = G_n(5), where G_n(k) is the Goodstein function defined in A266201. A266204

Weak Goodstein numbers: a(n) = g_n(n), where g_n(n) is the weak Goodstein function. A266202

a(n) is the smallest m such that the elliptic curve x³ + y³ = m has rank n, or -1 if no such m exists. A60748

T(n,k)=Number of nXk 0..1 arrays with every element unequal to 1, 2, 3, 5 or 8 king-move adjacent elements, with upper left element zero. A305367

Numbers k for which rank of the elliptic curve y² = x³ - 432·k² is 4. A309964

Numbers k such that sopf(k) = sopf(k² - 1), where sopf(k) = A008472(k). A64019

Totally multiplicative sequence with a(p) = a(p-1) + 9 for prime p. A166706

Composite numbers for which the root mean square of proper divisors is an integer. A247135