Properties of the Number 2821

Two Thousand Eight Hundred Twenty-One

Basics

Value: 2820 → 2821 → 2822

Parity: odd

Prime: No

Previous Prime: 2819

Next Prime: 2833

Digit Sum: 13

Digital Root: 4

Palindrome: No

Factorization: 7 × 13 × 31

Divisors: 1, 7, 13, 31, 91, 217, 403, 2821

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

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Representations

Binary: 101100000101

Octal: 5405

Duodecimal: 1771

Hexadecimal: b05

Square: 7958041

Square Root: 53.113086899558006

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

Fermat pseudoprimes to base 2, also called Sarrus numbers or Poulet numbers. A1567

Carmichael numbers: composite numbers k such that a^k-1 == 1 (mod k) for every a coprime to k. A2997

Octagonal numbers: n*(3·n-2). Also called star numbers. A567

3-Carmichael numbers: Carmichael numbers equal to the product of 3 primes: k = p·q*r, where p < q < r are primes such that a^k-1 == 1 (mod k) if a is prime to k. A87788

Sum of divisors of square numbers. A65764

Ooguri-Vafa invariants of disk degeneracies for brane I or brane II in the O(K) -> P² geometry. A61637

Partial sums of A299266. A299267

Number of sublattices of index n in generic 3-dimensional lattice. A1001

Number of points of norm <= n² in square lattice. A328

Pseudoprimes to base 3. A5935