681
domain: N
Properties
Digital Properties
- Digit Count
- 3
- Digit Sum
- 15
- Digital Root
- 6
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 3
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 912
- Proper Divisor Sum (Aliquot Sum)
- 231
- 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
- 452
- Möbius Function
- 1
- Radical
- 681
- Omega Function (Ω)
- 2
- Little Omega Function (ω)
- 2
Special
- Factorial
- no
- Catalan Number
- no
- Bell Number
- no
- Motzkin Number
- no
- Primorial
- no
Figurate Numbers
- Fibonacci Number
- no
- Triangular Number
- no
- Perfect Square
- no
- Perfect Cube
- no
- Pentagonal Number
- no
- Hexagonal Number
- no
- 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
- 64
- Smith Number
- no
Primality
- Prime
- no
- Composite Number
- yes
- Semiprime
- yes
- 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
- no
Classification
- Even
- no
- Odd
- yes
Names
- German
- sechshunderteinundachtzig· ordinal: sechshunderteinundachtzigste
- English
- six hundred eighty-one· ordinal: six hundred eighty-first
- Spanish
- seiscientos ochenta y uno· ordinal: 681º
- French
- six cent quatre-vingt-un· ordinal: six cent quatre-vingt-unième
- Italian
- seicentoottantuno· ordinal: 681º
- Latin
- sescenti octoginta unus· ordinal: 681.
- Portuguese
- seiscentos e oitenta e um· ordinal: 681º
Appears in sequences
- A self-generating sequence: a(1)=1, a(2)=2, a(n+1) chosen so that a(n+1)-a(n-1) is the first number not obtainable as a(j)-a(i) for 1<=i<j<=n.at n=30A001149
- a(n) = 3 * prime(n).at n=48A001748
- Centered 4-dimensional orthoplex numbers (crystal ball sequence for 4-dimensional cubic lattice).at n=5A001846
- Crystal ball sequence for 5-dimensional cubic lattice.at n=4A001847
- a(n) = Sum_{k=0..n-1} binomial(n,k+1) * binomial(n+k,k).at n=5A002002
- MacMahon's generalized sum of divisors function.at n=15A002127
- a(n) = 3^n reduced modulo 2^n.at n=10A002380
- Number of non-isomorphic ways to attack all squares on an n X n chessboard using the smallest possible number of queens with each queen attacking at least one other.at n=10A002565
- Expansion of 1/((1-x)^3*(1-x^2)^2*(1-x^3)).at n=11A002625
- a(n) = a(n-1) + a(n-2) - a(n-3).at n=26A002798
- Sum a(n) x^n / n = log (1 + Sum g(n) x^n ), where g(n) is # graphs on n nodes (A000088).at n=5A003083
- Numbers that are the sum of 11 positive 5th powers.at n=29A003356
- Divisible only by primes congruent to 3 mod 7.at n=42A004621
- a(n) = floor(n*phi^6), phi = golden ratio, A001622.at n=38A004921
- Centered pentagonal numbers: (5n^2+5n+2)/2; crystal ball sequence for 3.3.3.4.4. planar net.at n=16A005891
- Number of trivalent connected (or cubic) planar graphs with 2n nodes.at n=7A005964
- McKay-Thompson series of class 7A for Monster.at n=4A007264
- Coordination sequence T3 for Zeolite Code AET.at n=18A008009
- Coordination sequence T3 for Zeolite Code AFS and BPH.at n=20A008025
- Coordination sequence T4 for Zeolite Code BRE.at n=17A008061