645
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
- 2
Divisibility
- Divisor Count
- 8
- Divisor Sum
- 1056
- Proper Divisor Sum (Aliquot Sum)
- 411
- 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
- 336
- Möbius Function
- -1
- Radical
- 645
- 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
- no
- Harshad Number
- yes
- Narcissistic Number
- no
- Collatz Steps
- 100
- Smith Number
- yes
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
- sechshundertfünfundvierzig· ordinal: sechshundertfünfundvierzigste
- English
- six hundred forty-five· ordinal: six hundred forty-fifth
- Spanish
- seiscientos cuarenta y cinco· ordinal: 645º
- French
- six cent quarante-cinq· ordinal: six cent quarante-cinqième
- Italian
- seicentoquarantacinque· ordinal: 645º
- Latin
- sescenti quadraginta quinque· ordinal: 645.
- Portuguese
- seiscentos e quarenta e cinco· ordinal: 645º
Appears in sequences
- Number of positive integers <= 2^n of form x^2 + 12 y^2.at n=12A000021
- a(n) = floor(n^2/3).at n=44A000212
- Number of trees of diameter 8.at n=5A000306
- Octagonal numbers: n*(3*n-2). Also called star numbers.at n=15A000567
- Generalized octagonal numbers: k*(3*k-2), k=0, +- 1, +- 2, +-3, ...at n=29A001082
- Fermat pseudoprimes to base 2, also called Sarrus numbers or Poulet numbers.at n=2A001567
- Expansion of (1+x^3)/((1-x)*(1-x^2)^2*(1-x^3)).at n=26A001973
- Number of partitions of floor(5n/2)-1 into n nonnegative integers each no more than 5.at n=16A001976
- Heptagonal (or 7-gonal) pyramidal numbers: a(n) = n*(n+1)*(5*n-2)/6.at n=9A002413
- Numbers that are the sum of 6 positive 4th powers.at n=49A003340
- Numbers that are the sum of 10 positive 7th powers.at n=5A003377
- From a nim-like game.at n=22A003412
- Divisors of 2^28 - 1.at n=17A003536
- Sum of remainders of n mod k, for k = 1, 2, 3, ..., n.at n=60A004125
- Numbers that are the sum of at most 10 positive 7th powers.at n=50A004872
- Numbers that are the sum of at most 11 positive 7th powers.at n=55A004873
- a(n) = floor(n*phi^6), phi = golden ratio, A001622.at n=36A004921
- Triangular numbers plus quarter squares: n*(n+1)/2 + floor(n^2/4) (i.e., A000217(n) + A002620(n)).at n=29A006578
- Smith (or joke) numbers: composite numbers k such that sum of digits of k = sum of digits of prime factors of k (counted with multiplicity).at n=29A006753
- Binary palindromes: numbers whose binary expansion is palindromic.at n=51A006995