Properties of the Number 21906

Twenty-One Thousand Nine Hundred Six

Basics

Value: 21905 → 21906 → 21907

Parity: even

Prime: No

Previous Prime: 21893

Next Prime: 21911

Digit Sum: 18

Digital Root: 9

Palindrome: No

Factorization: 2 × 3 ² × 1217

Divisors: 1, 2, 3, 6, 9, 18, 1217, 2434, 3651, 7302

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

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Representations

Binary: 101010110010010

Octal: 52622

Duodecimal: 10816

Hexadecimal: 5592

Square: 479872836

Square Root: 148.00675660252813

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

Coordination sequence for C₃ lattice: a(n) = 16·n² + 2 (n>0), a(0)=1. A10006

Numbers n for which 8·R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n. A96846

Numbers k such that (k / sum of digits of k) and (k+1 / sum of digits of k+1) are both prime. A85775

Numbers k such that k!!!!!! - 1 is prime. A51592

Number of (w,x,y,z) with all terms in {1,...,n} and w < (geometric mean of x,y,z). A212141

Length of n-th iterate of the mapping 00->0010, 01->010, 10->000, starting with 00. A289019

a(n) = least m such that sum of m reciprocal primes starting with n-th prime is >1. A137368

G.f. satisfies: A(x) = A(x/A(x))² - x. A241000

Numbers whose square and cube taken together contain each decimal digit at least twice. A363909

Numbers of the form k² + 2 that are the sums of two squares. A329170