Properties of the Number 21506

Twenty-One Thousand Five Hundred Six

Basics

Value: 21505 → 21506 → 21507

Parity: even

Prime: No

Previous Prime: 21503

Next Prime: 21517

Digit Sum: 14

Digital Root: 5

Palindrome: No

Factorization: 2 × 10753

Divisors: 1, 2, 10753, 21506

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

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Representations

Binary: 101010000000010

Octal: 52002

Duodecimal: 10542

Hexadecimal: 5402

Square: 462508036

Square Root: 146.64924138910504

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

Positive integers k such that (k+1)⁴ has a divisor congruent to -1 modulo k. A350916

Semiprimes in A056105. A113519

a(0) = 1, a(1) = 2, and a(n) = 23·a(n-1) - a(n-2) - 4 for n >= 2. A350917

Expansion of ∑_k>0 x^3·k/(1+x^k)⁴. A363617

Markoff spectrum N⁵(λ). A293173

Solution of the complementary equation a(n) = a(n-1) + a(n-2) + b(n-1) + b(n-2) - b(n-3), where a(0) = 1, a(1) = 3, a(2) = 5, b(0) = 2, b(1) = 4, b(2) = 6, and (a(n)) and (b(n)) are increasing complementary sequences. A295358

a(0) = 1, a(n) = 21·n² + 2 for n>0. A10011

Triangle read by rows: A007318^-1 * A136536. A136537

Number of 4 X n 0..1 arrays with rows and antidiagonals unimodal and columns nondecreasing. A224148

Partial sums of the number of active (ON, black) cells in n-th stage of growth of two-dimensional cellular automaton defined by "Rule 838", based on the 5-celled von Neumann neighborhood. A273681