405
domain: N
Properties
Digital Properties
- Digit Count
- 3
- Digit Sum
- 9
- Digital Root
- 9
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 1
Divisibility
- Divisor Count
- 10
- Divisor Sum
- 726
- Proper Divisor Sum (Aliquot Sum)
- 321
- 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
- 216
- Möbius Function
- 0
- Radical
- 15
- Omega Function (Ω)
- 5
- 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
- yes
- Narcissistic Number
- no
- Collatz Steps
- 27
- Smith Number
- no
Primality
- Prime
- no
- Composite Number
- yes
- Semiprime
- no
- Squarefree Number
- no
- 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
- yes
- Carmichael Number
- no
Classification
- Even
- no
- Odd
- yes
Names
- German
- vierhundertfünf· ordinal: vierhundertfünfste
- English
- four hundred five· ordinal: four hundred fifth
- Spanish
- cuatrocientos cinco· ordinal: 405º
- French
- quatre cent cinq· ordinal: quatre cent cinqième
- Italian
- quattrocentocinque· ordinal: 405º
- Latin
- quadringenti quinque· ordinal: 405.
- Portuguese
- quatrocentos e cinco· ordinal: 405º
Appears in sequences
- a(n) = n*(n+3)/2.at n=27A000096
- Let A(n) = #{(i,j,k): i^2 + j^2 + k^2 <= n}, V(n) = (4/3)Pi*n^(3/2), P(n) = A(n) - V(n); A000092 gives values of n where |P(n)| sets a new record; sequence gives (nearest integer to, I believe) P(A000092(n)).at n=24A000223
- a(1)=0; for n>1, a(n) = number of isomeric hydrocarbons of the acetylene series with carbon content n.at n=10A000642
- Numbers beginning with letter 'f' in English.at n=29A000867
- Numbers that are the sum of 4 cubes in more than 1 way.at n=22A001245
- Pentagonal pyramidal numbers: a(n) = n^2*(n+1)/2.at n=9A002411
- Numbers k such that (k^2 + 1)/2 is prime.at n=61A002731
- Number of integer points in a certain quadrilateral scaled by a factor of n.at n=29A002789
- The minimal sequence from solving n^3 - m^2 = a(n).at n=60A002938
- Numbers that are the sum of 3 positive cubes.at n=53A003072
- Numbers that are the sum of 5 positive 4th powers.at n=26A003339
- Numbers that are the sum of 10 positive 4th powers.at n=46A003344
- Numbers that are the sum of 8 positive 5th powers.at n=14A003353
- Roman numerals with 1 letter, in alphabetical order; then those with 2 letters, etc.at n=45A003588
- Numbers of the form 3^i*5^j with i, j >= 0.at n=15A003593
- Smallest positive integer that is n times its digit sum, or 0 if no such number exists.at n=44A003634
- Completely multiplicative with a(prime(k)) = prime(k+1).at n=47A003961
- Factorial numbers written backwards.at n=7A004153
- Numbers obtained by reversing digits of factorial numbers.at n=7A004192
- Primes written in base 6.at n=34A004680