2721
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 12
- Digital Root
- 3
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 3
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 3632
- Proper Divisor Sum (Aliquot Sum)
- 911
- 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
- 1812
- Möbius Function
- 1
- Radical
- 2721
- 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
- 66
- 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
- Bessel polynomials y_n(x) (see A001498) evaluated at 2.at n=4A001517
- Glaisher's function U(n).at n=8A002612
- Numerators of approximations to e.at n=20A006258
- Numerators of convergents to e.at n=10A007676
- Coordination sequence T6 for Zeolite Code DDR.at n=33A008076
- Expansion of 1/(1-x^10-x^11-x^12-x^13-x^14-x^15-x^16-x^17-x^18).at n=64A017894
- Numbers k such that the continued fraction for sqrt(k) has period 58.at n=8A020397
- Numbers k such that Fibonacci(k) == -2 (mod k).at n=43A023163
- a(n) = T(n, n-4), T given by A026519. Also a(n) = number of integer strings s(0), ..., s(n), counted by T, such that s(n) = 4.at n=8A026524
- a(n) = T(n,n-4), T given by A026536. Also a(n) = number of integer strings s(0), ..., s(n), counted by T, such that s(n) = 4.at n=8A026541
- Sequence satisfies T(a)=a, where T is defined below.at n=43A027597
- a(n+1) = Sum_{k=0..floor(2*n/5)} a(k) * a(n-k).at n=15A030037
- 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 34.at n=23A031532
- Numbers k such that the period of the continued fraction for sqrt(k) contains exactly 28 ones.at n=13A031796
- Number of partitions satisfying (cn(1,5) = cn(4,5) = 0 and cn(0,5) <= cn(2,5) and cn(0,5) <= cn(3,5)).at n=53A036825
- Smallest of three consecutive squarefree numbers k, k+1, k+2 of the form p*q where p and q are distinct primes.at n=33A039833
- Numbers k such that the string 5,3 occurs in the base 9 representation of k but not of k-1.at n=37A044299
- Numbers n such that string 2,1 occurs in the base 10 representation of n but not of n-1.at n=30A044353
- Numbers n such that string 5,3 occurs in the base 9 representation of n but not of n+1.at n=37A044680
- Numbers n such that string 2,1 occurs in the base 10 representation of n but not of n+1.at n=30A044734