8181
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
- 3
Divisibility
- Divisor Count
- 10
- Divisor Sum
- 12342
- Proper Divisor Sum (Aliquot Sum)
- 4161
- 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
- 5400
- Möbius Function
- 0
- Radical
- 303
- 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
- yes
- Harshad Number
- no
- Narcissistic Number
- no
- Collatz Steps
- 65
- 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
- From a problem in AI planning: a(n) = 4+a(n-1)+a(n-2)+a(n-3)+a(n-4)-a(n-5)-a(n-6)-a(n-7), n>7.at n=14A007800
- n is equal to the number of 1's in all numbers <= n written in base 8.at n=5A014885
- Number of partitions satisfying (cn(0,5) <= cn(1,5) = cn(4,5) and cn(0,5) <= cn(2,5) and cn(0,5) <= cn(3,5)).at n=49A036813
- Numbers whose base-4 representation contains exactly three 1's and four 3's.at n=14A045128
- Odd numbers with exactly 5 palindromic prime factors (counted with multiplicity).at n=31A046375
- Numbers whose consecutive digits differ by 7.at n=23A048409
- Numbers of the form (10*a + b)^2 + (10*b + a)^2 with a and b less than 10, in numerical order.at n=35A061191
- Expansion of (1 + 5*x - 12*x^2 - 80*x^3)/(1 - 33*x^2 + 272*x^4).at n=6A097113
- 2^p - 11 for p prime.at n=5A098231
- a(n) = 2^(n + 11) - 11.at n=2A098808
- Numbers missing from A102370.at n=12A102371
- a(1) = 999, a(n) is the number obtained by concatenating product of neighboring digits of the previous term.at n=1A110401
- a(n) = 1 + sum{p=primes<n, p does not divide n} a(p).at n=41A112479
- Triangle read by rows: T(n,k) is the number of deco polyominoes of height n and vertical height (i.e., number of rows) k (1 <= k <= n). A deco polyomino is a directed column-convex polyomino in which the height, measured along the diagonal, is attained only in the last column.at n=31A121692
- a(n) = 2^(n+1) - n + 1.at n=12A132753
- Number of ways to tile an n X 1 strip with 1 X 1 squares and 2 X 1 dominoes with the restriction that no three consecutive tiles are of the same type.at n=28A137200
- Values of x in solutions (x,y,z) to the Diophantine equation x^3-x^2+y^3-y^2=z^3-z^2, with 1<x<y<z.at n=21A138667
- a(n) is the least odd number 2^n - m minimizing A007947(m*(2^n - m)).at n=12A143701
- Partial sums of A164095.at n=18A164096
- Number of n X n 1..4 arrays with all 1s connected, all 2s connected, all 3s connected, all 4s connected, 1 in the upper left corner, 2 in the upper right corner, 3 in the lower left corner, and 4 in the lower right corner.at n=2A164748