15905
domain: N
Properties
Digital Properties
- Digit Count
- 5
- Digit Sum
- 20
- Digital Root
- 2
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 1
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 19092
- Proper Divisor Sum (Aliquot Sum)
- 3187
- Abundant Number
- no
- Perfect Number
- no
- Deficient Number
- yes
- Weird Number
- no
- Untouchable Number
- no
- Primitive Abundant
- no
Derived Values
- Euler's Totient
- 12720
- Möbius Function
- 1
- Radical
- 15905
- Omega Function (Ω)
- 2
- 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
- 102
- Smith Number
- no
- Vampire Number
- no
Primality
- Prime
- no
- Composite Number
- yes
- Semiprime
- yes
- 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
Appears in sequences
- Numbers n such that n | 10^n + 9^n + 1.at n=32A057295
- Nonprime integers n such that n divides A120492(n).at n=35A120329
- Numbers k such that 10*(11*10^k-1) + 3 is prime or PRP.at n=20A123383
- a(n) = 8*a(n-1)+49*a(n-2), n>2 ; a(0)=1, a(1)=1, a(2)=8 .at n=5A155460
- a(n) = 1 + n + ((n-1)*n^2)/2.at n=32A218152
- a(n) = ceiling(li(2*2^n) - li(2^n)) - (pi(2*2^n) - pi(2^n)) with li(x) the logarithmic integral and pi(x) the prime counting function.at n=38A223853
- Curvature (rounded down) of the circle inscribed in the n-th golden triangle arranged in a spiral form.at n=18A228560
- Number of partitions p of n such that 1 + (1/2)*max(p) is a part of p.at n=45A238625
- Number of (n+2)X(2+2) 0..1 arrays with no 3x3 subblock diagonal sum 1 and no antidiagonal sum 2 and no row sum 0 and no column sum 3.at n=15A255795
- Number of nX4 0..1 arrays with every element equal to 0, 1, 3 or 5 horizontally, diagonally or antidiagonally adjacent elements, with upper left element zero.at n=9A302423
- The number of digits of the greatest product from addends that sum up to 10^n.at n=5A309440
- Quasi-Repfigit numbers (or Quasi-Keith numbers).at n=18A319746
- Stellated octagon numbers: a(n) = 20*n^2 + 8*n + 1.at n=28A381196