685
domain: N
Properties
Digital Properties
- Digit Count
- 3
- Digit Sum
- 19
- Digital Root
- 1
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 828
- Proper Divisor Sum (Aliquot Sum)
- 143
- 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
- 544
- Möbius Function
- 1
- Radical
- 685
- 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
- 126
- 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
- sechshundertfünfundachtzig· ordinal: sechshundertfünfundachtzigste
- English
- six hundred eighty-five· ordinal: six hundred eighty-fifth
- Spanish
- seiscientos ochenta y cinco· ordinal: 685º
- French
- six cent quatre-vingt-cinq· ordinal: six cent quatre-vingt-cinqième
- Italian
- seicentoottantacinque· ordinal: 685º
- Latin
- sescenti octoginta quinque· ordinal: 685.
- Portuguese
- seiscentos e oitenta e cinco· ordinal: 685º
Appears in sequences
- a(n) = ceiling(n^2/2).at n=37A000982
- a(n) = a(n-2) + a(n-5).at n=37A001687
- Primes multiplied by 5.at n=32A001750
- Centered square numbers: a(n) = 2*n*(n+1)+1. Sums of two consecutive squares. Also, consider all Pythagorean triples (X, Y, Z=Y+1) ordered by increasing Z; then sequence gives Z values.at n=18A001844
- a(1) = 1; for n>1, a(n) = a(n-1) + 1 + sum of distinct prime factors of a(n-1) that are < a(n-1).at n=37A003508
- Expansion of tan(x)*cosh(x).at n=3A003719
- a(n) = ceiling(n*phi^9), where phi is the golden ratio, A001622.at n=9A004964
- Number of binary words of length n in which the ones occur only in blocks of length at least 4.at n=17A005253
- Number of unrooted triangulations of a disk with 2 internal nodes and n+3 nodes on the boundary.at n=5A005504
- a(n) = a(n-1) + (-1)^(n-1) * a(n-2)^2 for n >= 2 with a(0) = 0 and a(1) = 1.at n=10A005605
- Numerators of approximations to e.at n=15A006258
- Record number of steps to reach 1 in '3x+1' problem, corresponding to starting values in A006877.at n=53A006878
- Numbers that are the sum of 2 nonzero squares in 2 or more ways.at n=45A007692
- Number of non-Abelian metacyclic groups of order 2^n.at n=26A007982
- Crystal ball sequence for planar net 3.6.3.6.at n=17A008580
- E.g.f. tan(x)*exp(x).at n=7A009739
- Coordination sequence T2 for Zeolite Code RTH.at n=18A009894
- Number of Barlow packings that repeat after exactly n layers.at n=16A011768
- a(n) = floor(n*(n - 1)*(n - 2)/32).at n=29A011914
- tan(arcsinh(x)+log(x+1))=2*x-1/2!*x^2+17/3!*x^3-54/4!*x^4+685/5!*x^5...at n=5A013072