Properties of the Number 666

Six Hundred Sixty-Six

Basics

Value: 665 → 666 → 667

Parity: even

Prime: No

Previous Prime: 661

Next Prime: 673

Digit Sum: 18

Digital Root: 9

Palindrome: Yes

Factorization: 2 × 3 ² × 37

Divisors: 1, 2, 3, 6, 9, 18, 37, 74, 111, 222

Polygonal

Triangular: Yes

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

Today's Target

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Representations

Binary: 1010011010

Octal: 1232

Duodecimal: 476

Hexadecimal: 29a

Square: 443556

Square Root: 25.80697580112788

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

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

Repdigit numbers, or numbers whose digits are all equal. A10785

Sum of squares of the first n primes. A24450

Numbers k such that the k-th triangular number contains only digits {0,1,2}. A119034

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

Smith (or joke) numbers: composite numbers k such that sum of digits of k = sum of digits of prime factors of k (counted with multiplicity). A6753

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

Doubly triangular numbers: a(n) = n*(n+1)*(n²+n+2)/8. A2817

Numbers whose ternary expansion contains no 1's. A5823