2105
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 8
- Digital Root
- 8
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 1
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 2532
- Proper Divisor Sum (Aliquot Sum)
- 427
- 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
- 1680
- Möbius Function
- 1
- Radical
- 2105
- 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
- 125
- 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
- Number of symmetric ways of folding a strip of n labeled stamps.at n=8A000560
- Erdős-Selfridge function: a(n) is the least number m > n+1 such that the least prime factor of binomial(m, n) is > n.at n=24A003458
- a(n) = 3*n^2 + 3*n - 1.at n=26A004538
- Numbers n such that n! has a square number of digits.at n=36A006488
- Molien series for alternating group Alt_8 (or A_8).at n=29A008631
- Pseudoprimes to base 29.at n=23A020157
- Fibonacci sequence beginning 1, 14.at n=12A022104
- Numbers with exactly 6 2's in their ternary expansion.at n=5A023704
- Base 6 expansion uses each positive digit just once.at n=8A023744
- Index of 6^n within the sequence of the numbers of the form 3^i*6^j.at n=50A025713
- a(n) = sum of the numbers between the two n's in A026354.at n=42A026357
- Number of proper factorizations of p1^n*p2^2, where p1 and p2 are distinct primes.at n=15A031125
- Numbers k such that the continued fraction for sqrt(k) has even period and if the last term of the periodic part is deleted the central term is 18.at n=42A031516
- Numbers of the form (q^2+(q+1)^2)*(r^2+(r+1)^2), q,r >= 1.at n=23A033682
- Composite numbers k, not a power of 2, such that the E(k) == 1 (mod k), where E(k) is the k-th Euler number (A000364).at n=15A035163
- Numbers k such that gcd(phi(k), k-1) = number of divisors of (k-1).at n=44A039768
- Denominators of continued fraction convergents to sqrt(302).at n=9A041569
- Numerators of continued fraction convergents to sqrt(879).at n=6A042698
- a(n)=(s(n)+4)/8, where s(n)=n-th base 8 palindrome that starts with 4.at n=25A043068
- Numbers n such that string 7,1 occurs in the base 8 representation of n but not of n-1.at n=36A044244