665
domain: N
Properties
Digital Properties
- Digit Count
- 3
- Digit Sum
- 17
- Digital Root
- 8
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 8
- Divisor Sum
- 960
- Proper Divisor Sum (Aliquot Sum)
- 295
- 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
- 432
- Möbius Function
- -1
- Radical
- 665
- 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
- 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
- yes
- Harshad Number
- no
- Narcissistic Number
- no
- Collatz Steps
- 51
- 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
- no
Classification
- Even
- no
- Odd
- yes
Names
- German
- sechshundertfünfundsechzig· ordinal: sechshundertfünfundsechzigste
- English
- six hundred sixty-five· ordinal: six hundred sixty-fifth
- Spanish
- seiscientos sesenta y cinco· ordinal: 665º
- French
- six cent soixante-cinq· ordinal: six cent soixante-cinqième
- Italian
- seicentosessantacinque· ordinal: 665º
- Latin
- sescenti sexaginta quinque· ordinal: 665.
- Portuguese
- seiscentos e sessenta e cinco· ordinal: 665º
Appears in sequences
- a(n) = n*(n+3)/2.at n=35A000096
- a(0) = 1, a(1) = 4, and a(n) = a(n-1) + a(n-2) for n >= 2.at n=12A000285
- a(n) = 3^n - 2^n.at n=6A001047
- Triangle of values of 2-d recurrence.at n=46A001404
- Numbers k such that 19*2^k - 1 is prime.at n=15A001775
- Class numbers associated with terms of A001986.at n=20A001987
- Class numbers associated with terms of A001986.at n=19A001987
- Numbers dividing A002037(i) and larger than A002037(i-1), for some i>0.at n=55A002038
- Odd squarefree numbers with an odd number of prime factors that have no prime factors greater than 31.at n=32A002556
- Ferromagnetic susceptibility series for f.c.c. lattice.at n=18A002924
- Expansion of 1/((1-2x)(1+x^2)(1-x-2x^3)).at n=8A003477
- Divisors of 2^36 - 1.at n=49A003543
- a(n) = n^2 + prime(n).at n=23A004232
- Number of n-dimensional unimodular lattices (or quadratic forms).at n=25A005134
- a(n) = floor(e^((n-1)/2)).at n=14A005182
- a(n) = (n-1)*n*(n+4)/6.at n=15A005581
- Denominators of convergents to log_2 3.at n=8A005664
- Number of partitions of n into Fibonacci parts (with 2 types of 1).at n=19A007000
- a(n) = a(n-2) + a(n-3), with a(0) = 0, a(1) = 1, a(2) = 2.at n=24A007307
- Coordination sequence T3 for Zeolite Code AFO.at n=17A008017