9090
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 18
- Digital Root
- 9
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 1
Divisibility
- Divisor Count
- 24
- Divisor Sum
- 23868
- Proper Divisor Sum (Aliquot Sum)
- 14778
- Abundant Number
- yes
- Perfect Number
- no
- Deficient Number
- no
- Highly Composite
- no
- Weird Number
- no
- Untouchable Number
- no
- Primitive Abundant
- no
Derived Values
- Euler's Totient
- 2400
- Möbius Function
- 0
- Radical
- 3030
- Omega Function (Ω)
- 5
- Little Omega Function (ω)
- 4
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
- 140
- Smith Number
- no
- Vampire 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
- no
- Carmichael Number
- no
Classification
- Even
- yes
- Odd
- no
Appears in sequences
- Minimal number of people to give a 50% probability of having at least n coincident birthdays in one year.at n=40A014088
- a(n) = n*(9*n - 1)/2.at n=45A022266
- 2nd elementary symmetric function of first n+1 positive integers congruent to 1 mod 3.at n=8A024212
- Expansion of 1/((1-4x)(1-6x)(1-9x)(1-11x)).at n=3A028140
- Theta series of 10-dimensional 2-modular lattice of minimal norm 2.at n=8A029545
- a(n) = floor(10^5/n).at n=10A033427
- Number of different products of partitions of n; number of partitions of n into prime parts (1 included); number of distinct orders of Abelian subgroups of symmetric group S_n.at n=51A034891
- Number of centered 6-valent trees with n nodes.at n=16A036651
- Differences of A038011.at n=3A038012
- Numerators of continued fraction convergents to sqrt(912).at n=2A042762
- Triangle giving coefficients of ménage hit polynomials.at n=49A058057
- Coefficients of ménage hit polynomials.at n=4A058085
- Values of m such that N = (am+1)(bm+1)(cm+1) is a 3-Carmichael number (A087788), where a,b,c = 1,2,3.at n=44A064238
- Values of m such that N=(am+1)(bm+1)(cm+1) is a 3-Carmichael number (A087788), where a,b,c = 1,2,11.at n=5A064242
- Values of m such that N=(am+1)(bm+1)(cm+1) is a 3-Carmichael number (A087788), where a,b,c = 1,2,29.at n=1A064251
- Values of m such that N = (am+1)(bm+1)(cm+1) is a 3-Carmichael number (A087788), where a,b,c = 1,2,57.at n=3A065697
- 1/n has period 4 in base 10.at n=35A069858
- Expansion of (5 + 6*x + 3*x^2 - 2*x^3) / (1 - 2*x - 2*x^2 - 2*x^3 + x^4) in powers of x.at n=7A071101
- Numbers which are either a divisor or a multiple of their 9's complement.at n=27A084020
- Arrange n^2 octagons that each have area 7 so that they leave (n-1)^2 square gaps each with area 2; a(n) is the total area of these polygons.at n=31A086640