Properties of the Number 820

Eight Hundred Twenty

Basics

Value: 819 → 820 → 821

Parity: even

Prime: No

Previous Prime: 811

Next Prime: 821

Digit Sum: 10

Digital Root: 1

Palindrome: No

Factorization: 2 ² × 5 × 41

Divisors: 1, 2, 4, 5, 10, 20, 41, 82, 164, 205

Polygonal

Triangular: Yes

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

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Representations

Binary: 1100110100

Octal: 1464

Duodecimal: 584

Hexadecimal: 334

Square: 672400

Square Root: 28.635642126552707

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

Triangular numbers: a(n) = binomial(n+1,2) = n*(n+1)/2 = 0 + 1 + 2 + ... + n. A217

a(n) = sigma₂(n): sum of squares of divisors of n. A1157

List of totally balanced sequences of 2n binary digits written in base 10. Binary expansion of each term contains n 0's and n 1's and reading from left to right (the most significant to the least significant bit), the number of 0's never exceeds the number of 1's. A14486

Second hexagonal numbers: a(n) = n*(2·n + 1). A14105

Number of partitions of n into parts 5k+2 or 5k+3. A3106

Sum of positive integers in smallest positive reduced residue system modulo n. a(1) = 1 by convention. A23896

a(n) = (9ⁿ - 1)/8. A2452

Triangular array: T(n,k) counts the partitions of the set [n] into k odd sized blocks. A136630

a(n) = binomial(n,2): number of size-2 subsets of {0,1,...,n} that contain no consecutive integers. A161680

a(n) = ∑_d∣n (-1)^d-1*d². A321543