Properties of the Number 645

Six Hundred Forty-Five

Basics

Value: 644 → 645 → 646

Parity: odd

Prime: No

Previous Prime: 643

Next Prime: 647

Digit Sum: 15

Digital Root: 6

Palindrome: No

Factorization: 3 × 5 × 43

Divisors: 1, 3, 5, 15, 43, 129, 215, 645

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

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Representations

Binary: 1010000101

Octal: 1205

Duodecimal: 459

Hexadecimal: 285

Square: 416025

Square Root: 25.39685019840059

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

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

Binary palindromes: numbers whose binary expansion is palindromic. A6995

Generalized octagonal numbers: k*(3·k-2), k=0, +- 1, +- 2, +-3, ... A1082

Number of partitions of n into nonzero triangular numbers. A7294

Number of "ON" cells at n-th stage in the "Ulam-Warburton" two-dimensional cellular automaton. A147562

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

Sum of remainders of n mod k, for k = 1, 2, 3, ..., n. A4125

a(n) = floor(n²/3). A212

Coordination sequence for "cab" 3D uniform tiling formed from octahedra and truncated cubes. A299266