Properties of the Number 21905

Twenty-One Thousand Nine Hundred Five

Basics

Value: 21904 → 21905 → 21906

Parity: odd

Prime: No

Previous Prime: 21893

Next Prime: 21911

Digit Sum: 17

Digital Root: 8

Palindrome: No

Factorization: 5 × 13 × 337

Divisors: 1, 5, 13, 65, 337, 1685, 4381, 21905

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

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Representations

Binary: 101010110010001

Octal: 52621

Duodecimal: 10815

Hexadecimal: 5591

Square: 479829025

Square Root: 148.00337833982033

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(1)=3; for n > 1, a(n) = 1 + a(n-1) + gcd( a(n-1)*(a(n-1)+2), A073829(a(n-1)) ). A167053

Numbers of the form m² + 1 that can be expressed in more than one way as j² + k² with j > k > 1. A299708

Column 2 of triangle in A288180. A333281

Numbers of the form m² + 1 that can be expressed in more than one way as j² + k² with j > k > 1 and gcd(j,k) = 1. A300166

a(n) is the total number of squares after n iterations of the "Square Multiscale" substitution. A329919

a(n) = 16·n² + 1. A108211

a(n) = 81·n² - 90·n + 26. A154295

G.f. satisfies A(x) = 1 + x·A(x) / (1 - x²*A(x)⁵). A365693

Numbers k such that 80·R_k + 7 is prime, where R_k = 11...1 is the repunit (A002275) of length k. A56695

Main diagonal of A332365. A332366