15681
domain: N
Properties
Digital Properties
- Digit Count
- 5
- Digit Sum
- 21
- Digital Root
- 3
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 20912
- Proper Divisor Sum (Aliquot Sum)
- 5231
- Abundant Number
- no
- Perfect Number
- no
- Deficient Number
- yes
- Weird Number
- no
- Untouchable Number
- no
- Primitive Abundant
- no
Derived Values
- Euler's Totient
- 10452
- Möbius Function
- 1
- Radical
- 15681
- 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
- 53
- 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 k such that the period of the continued fraction for sqrt(k) contains exactly 72 ones.at n=23A031840
- Numbers whose base-5 representation contains exactly three 0's and three 1's.at n=16A045172
- Numbers k such that k^2 contains exactly 9 different digits.at n=23A054037
- Numbers whose square is a zeroless pandigital number (i.e., use the digits 1 through 9 once).at n=4A071519
- Triangular matrix T, read by rows, that satisfies T^2 = A105615^3; also equals the matrix cube of triangle A105623.at n=23A105626
- Where records appear in A109734.at n=34A109740
- Consider the array T(n, m) where the n-th row is the sequence of integer coefficients of A(x), where 1<=a(n)<=n, such that A(x)^(1/n) consists entirely of integer coefficients and where m is the (m+1)-th coefficient. This is the row sum of A to the first coefficient of one.at n=34A112285
- Absolute value of coefficient of X^2 in the characteristic polynomial of the n-th power of the matrix M = {{1,1,1,1,1}, {1,0,0,0,0}, {0,1,0,0,0}, {0,0,1,0,0}, {0,0,0,1,0}}.at n=24A123126
- Numbers whose square is a permutational number A134640.at n=46A134742
- Number of n X n binary arrays symmetric under 90 degree rotation with all ones connected only in a 1100-0111-0001 pattern in any orientation.at n=13A146664
- a(n) = 20*n^2 + 1.at n=28A158493
- a(n) = 80*n^2 + 1.at n=14A158776
- Number of arrays of n integers in -4..4 with sum zero and equal numbers of elements greater than zero and less than zero.at n=5A201807
- T(n,k)=Number of arrays of n integers in -k..k with sum zero and equal numbers of elements greater than zero and less than zero.at n=41A201811
- Number of arrays of 6 integers in -n..n with sum zero and equal numbers of elements greater than zero and less than zero.at n=3A201814
- Semiprimes of the form 5*n^2 + 1.at n=17A212707
- Smallest magic sum of an order-n magic square composed of consecutive Smith numbers.at n=7A213689
- Number of bangbangs (!!) in shell substitution when starting with : '!!' and : "!!" '!!'.at n=7A228162
- Number of compositions c of n such that no three points (i,c_i), (j,c_j), (k,c_k) are collinear, where c_i denotes the i-th part.at n=21A238686
- 7-step Fibonacci sequence starting with (0,0,0,0,0,1,0).at n=21A251710