Properties of the Number 561

Five Hundred Sixty-One

Basics

Value: 560 → 561 → 562

Parity: odd

Prime: No

Previous Prime: 557

Next Prime: 563

Digit Sum: 12

Digital Root: 3

Palindrome: No

Factorization: 3 × 11 × 17

Divisors: 1, 3, 11, 17, 33, 51, 187, 561

Polygonal

Triangular: Yes

Square: No

Pentagonal: No

Hexagonal: Yes

Heptagonal: No

Tetrahedral: No

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Representations

Binary: 1000110001

Octal: 1061

Duodecimal: 3A9

Hexadecimal: 231

Square: 314721

Square Root: 23.68543856465402

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

Hexagonal numbers: a(n) = n*(2·n-1). A384

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

Binary palindromes: numbers whose binary expansion is palindromic. A6995

Number of ordered triples (w,x,y) with all terms in {-n,...,0,...,n} and w² + x·y = 0. A211422

Centered icosahedral (or cuboctahedral) numbers, also crystal ball sequence for f.c.c. lattice. A5902

Multiples of 11. A8593

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

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