Properties of the Number 21205

Twenty-One Thousand Two Hundred Five

Basics

Value: 21204 → 21205 → 21206

Parity: odd

Prime: No

Previous Prime: 21193

Next Prime: 21211

Digit Sum: 10

Digital Root: 1

Palindrome: No

Factorization: 5 × 4241

Divisors: 1, 5, 4241, 21205

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

Today's Target

2196 Try Today's Challenge

Representations

Binary: 101001011010101

Octal: 51325

Duodecimal: 10331

Hexadecimal: 52d5

Square: 449652025

Square Root: 145.6193668438371

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

Integers k such that 10^k + 31 is prime. A107083

a(n) = a(n-1) + 2·a(n-3) with a(0)=a(1)=1, a(2)=3. A3229

Expansion of 1/(1-x-2·x³). A77949

Positive numbers y such that y² is of the form x² + (x + 569)² with integer x. A160090

Expansion of 1/(1+x+2·x³). A77974

a(n) = A192809(n)/2. A192811

Where records occur in A169784. A175437

Number of lower triangular n X n arrays colored with integers 0 upwards introduced in row major order, with no element equal to any horizontal, vertical, diagonal or antidiagonal neighbor, and containing the value n(n+1)/2-2. A211911

Number of nX3 0..1 arrays with every element unequal to 0, 1, 2, 6 or 7 king-move adjacent elements, with upper left element zero. A305035

Sequence from expansion of Cartan E₁₁ 12 state root sum zero characteristic polynomial: p(x)=1/(-1 + 274 x² - 3480 x³ + 21205 x⁴ - 76696 x⁵ + 175891x⁶ - 259324 x⁷ + 240551 x⁸ - 131824 x⁹ + 37101 x¹⁰ - 3676 x¹¹ - 44 x¹²). A143076