13021
domain: N
Properties
Digital Properties
- Digit Count
- 5
- Digit Sum
- 7
- Digital Root
- 7
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 1
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 13500
- Proper Divisor Sum (Aliquot Sum)
- 479
- Abundant Number
- no
- Perfect Number
- no
- Deficient Number
- yes
- Weird Number
- no
- Untouchable Number
- no
- Primitive Abundant
- no
Derived Values
- Euler's Totient
- 12544
- Möbius Function
- 1
- Radical
- 13021
- 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
- 76
- 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
- Pseudoprimes to base 5.at n=23A005936
- Expansion of e.g.f.: cos(tan(x)+log(x+1))=1-4/2!*x^2+6/3!*x^3-19/4!*x^4+20/5!*x^5...at n=8A012928
- a(n) = (1 - (-5)^n)/6.at n=6A014986
- Triangle of q-binomial coefficients for q=-5.at n=29A015113
- Triangle of q-binomial coefficients for q=-5.at n=34A015113
- Gaussian binomial coefficient [ n,6 ] for q = -5.at n=1A015327
- Linear 2nd order recurrence: a(n) = 4*a(n-1) + 5*a(n-2).at n=7A015531
- Cyclotomic polynomials at x=5.at n=14A019323
- Pseudoprimes to base 90.at n=23A020218
- Strong pseudoprimes to base 5.at n=5A020231
- Strong pseudoprimes to base 25.at n=11A020251
- Numbers k such that the continued fraction for sqrt(k) has period 95.at n=9A020434
- Cyclotomic polynomials at x=-5.at n=7A020504
- a(n) = n*(31*n-1)/2.at n=29A022288
- Numbers k such that the continued fraction for sqrt(k) has odd period and if the last term of the periodic part is deleted the two central terms are both 45.at n=0A031633
- Decimal expansion of a(n) is given by the first n terms of the periodic sequence with initial period 1,3,0,2.at n=4A037708
- a(n) = n^6 - n^5 + n^4 - n^3 + n^2 - n + 1.at n=5A060888
- Square array T(n,k) = (n^k - (-1)^k)/(n+1), n >= 0, k >= 0, read by falling antidiagonals.at n=83A062160
- Zsigmondy numbers for a = 5, b = 1: Zs(n, 5, 1) is the greatest divisor of 5^n - 1^n (A024049) that is relatively prime to 5^m - 1^m for all positive integers m < n.at n=13A064081
- Numbers n of the form k + reverse(k) for exactly three k.at n=30A071914