1809
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
- 8
- Divisor Sum
- 2720
- Proper Divisor Sum (Aliquot Sum)
- 911
- 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
- 1188
- Möbius Function
- 0
- Radical
- 201
- Omega Function (Ω)
- 4
- 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
- 55
- 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
- no
- Odd
- yes
Appears in sequences
- a(n) = ceiling(exp((n-1)/2)).at n=16A005181
- a(n) = n*(5*n - 1)/2.at n=27A005476
- Expansion of Product_{m>=1} (1 + q^m)^(-8).at n=8A007259
- Coefficients of completely replicable function "6d".at n=24A007263
- Coordination sequence T3 for Zeolite Code AFT.at n=32A008028
- Coordination sequence T4 for Zeolite Code MEI.at n=31A008149
- Year of birth of n-th President of U.S.A.at n=15A008745
- Expansion of (1+x^7)/((1-x)*(1-x^2)*(1-x^3)*(1-x^4)).at n=49A008768
- "Pascal sweep" for k=10: draw a horizontal line through the 1 at C(k,0) in Pascal's triangle; rotate this line and record the sum of the numbers on it (excluding the initial 1).at n=20A009550
- Expansion of ((theta_2)^4 + (theta_3)^4) / eta(z/2)^4.at n=4A014705
- Numbers k such that the continued fraction for sqrt(k) has period 38.at n=10A020377
- a(n) is least k such that k and 9k are anagrams in base n (written in base 10).at n=27A023101
- Number of partitions of n into distinct parts >= 5.at n=65A025150
- T(2n,n), T given by A026568.at n=6A026574
- T(n,[ n/2 ]), T given by A026568.at n=12A026579
- Number of partitions of n into distinct parts, the least being 4.at n=69A026825
- Diagonal sum of right-justified array T given by A027023.at n=10A027038
- Number of partitions of n that do not contain 6 as a part.at n=26A027340
- Sequence satisfies T^2(a)=a, where T is defined below.at n=43A027589
- a(n) = n^2 + n + 3.at n=42A027688