561
domain: N
Properties
Digital Properties
- Digit Count
- 3
- Digit Sum
- 12
- Digital Root
- 3
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 8
- Divisor Sum
- 864
- Proper Divisor Sum (Aliquot Sum)
- 303
- Abundant Number
- no
- Perfect Number
- no
- Deficient Number
- yes
- Highly Composite
- no
- Weird Number
- no
- Untouchable Number
- no
- Primitive Abundant
- no
Derived Values
- Euler's Totient
- 320
- Möbius Function
- -1
- Radical
- 561
- Omega Function (Ω)
- 3
- Little Omega Function (ω)
- 3
Special
- Factorial
- no
- Catalan Number
- no
- Bell Number
- no
- Motzkin Number
- no
- Primorial
- no
Figurate Numbers
- Fibonacci Number
- no
- Triangular Number
- yes
- Perfect Square
- no
- Perfect Cube
- no
- Pentagonal Number
- no
- Hexagonal Number
- yes
- Lucas Number
- no
- Tetrahedral Number
- no
- Pell Number
- no
- Tribonacci Number
- no
- Pronic Number
- no
Recreational
- Happy Number
- no
- Harshad Number
- no
- Narcissistic Number
- no
- Collatz Steps
- 43
- Smith Number
- no
Primality
- Prime
- no
- Composite Number
- yes
- Semiprime
- no
- Squarefree Number
- yes
- Prime Power
- no
- Prime Factorization
- no
- Twin Prime
- no
- Mersenne Prime
- no
- Sophie Germain Prime
- no
- Safe Prime
- no
- Powerful Number
- no
- Achilles Number
- no
- Perfect Power
- no
- Smooth Number
- no
- Carmichael Number
- yes
Classification
- Even
- no
- Odd
- yes
Names
- German
- fünfhunderteinundsechzig· ordinal: fünfhunderteinundsechzigste
- English
- five hundred sixty-one· ordinal: five hundred sixty-first
- Spanish
- quinientos sesenta y uno· ordinal: 561º
- French
- cinq cent soixante et un· ordinal: cinq cent soixante et unième
- Italian
- cinquecentosessantuno· ordinal: 561º
- Latin
- quingenti sexaginta unus· ordinal: 561.
- Portuguese
- quinhentos e sessenta e um· ordinal: 561º
Appears in sequences
- Number of partitions into non-integral powers.at n=13A000327
- Hexagonal numbers: a(n) = n*(2*n-1).at n=17A000384
- Number of 6-level labeled rooted trees with n leaves.at n=4A000405
- Number of numbers == 0 (mod 3) in range 2^n to 2^(n+1) with odd number of 1's in binary expansion.at n=11A000773
- Number of twin prime pairs < square of n-th prime.at n=43A000885
- Fermat pseudoprimes to base 2, also called Sarrus numbers or Poulet numbers.at n=1A001567
- Numbers dividing A002037(i) and larger than A002037(i-1), for some i>0.at n=48A002038
- Odd squarefree numbers with an odd number of prime factors that have no prime factors greater than 31.at n=26A002556
- a(0) = 1; for n > 0, a(n) = a(n-1) + floor(sqrt(a(n-1))).at n=50A002984
- Carmichael numbers: composite numbers k such that a^(k-1) == 1 (mod k) for every a coprime to k.at n=0A002997
- Dimensions of split simple Lie algebras over any field of characteristic zero.at n=52A003038
- Numbers that are the sum of 6 positive 4th powers.at n=41A003340
- Number of nonequivalent dissections of an n-gon into 3 polygons by nonintersecting diagonals up to rotation.at n=16A003451
- Number of nonequivalent dissections of an n-gon into 3 polygons by nonintersecting diagonals up to rotation and reflection.at n=20A003453
- Divisors of 2^40 - 1.at n=27A003546
- Tetrahedral numbers written backwards.at n=9A004161
- Number of partitions of 1/n into 3 reciprocals of positive integers.at n=54A004194
- Triangular numbers together with squares (excluding 0).at n=53A005214
- Number of n-bead bracelets (turnover necklaces) of two colors with 6 red beads and n-6 black beads.at n=12A005513
- Number of n-bead bracelets (turnover necklaces) with 12 red beads.at n=6A005516