Properties of the Number 821

Eight Hundred Twenty-One

Basics

Value: 820 → 821 → 822

Parity: odd

Prime: Yes

Previous Prime: 811

Next Prime: 823

Digit Sum: 11

Digital Root: 2

Palindrome: No

Factorization: 821

Divisors: 1, 821

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

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Representations

Binary: 1100110101

Octal: 1465

Duodecimal: 585

Hexadecimal: 335

Square: 674041

Square Root: 28.653097563788805

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

Lesser of twin primes. A1359

Primes of the form x² + xy + 2y², with·and y nonnegative. A106856

Central polygonal numbers (the Lazy Caterer's sequence): n(n+1)/2 + 1; or, maximal number of pieces formed when slicing a pancake with n cuts. A124

Primes of the form 2x² + 2xy + 17y². A139827

Prime quadruples: numbers k such that k, k+2, k+6, k+8 are all prime. A7530

Primes of the form 10·n+1. A30430

Initial members of prime triples (p, p+2, p+6). A22004

Indices k such that (1/3)*(prime(k)+prime(k+1)+prime(k+2)) is a prime. A64113

Irregular primes: primes p such that at least one of the numerators of the Bernoulli numbers B₂, B₄, ..., B_p-3 (A000367) is divisible by p. A928

Primes such that their decimal representations interpreted in base 11 are also prime. A91924