2181
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
- 2
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 2912
- Proper Divisor Sum (Aliquot Sum)
- 731
- 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
- 1452
- Möbius Function
- 1
- Radical
- 2181
- 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
- yes
- Harshad Number
- no
- Narcissistic Number
- no
- Collatz Steps
- 45
- 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 k, k+1 and k+2 have the same number of divisors.at n=42A005238
- Coordination sequence T2 for Zeolite Code MEI.at n=34A008147
- Coordination sequence T4 for Zeolite Code MOR.at n=30A008185
- Coordination sequence T1 for Zeolite Code MTN.at n=28A008186
- Coordination sequence T2 for Zeolite Code THO.at n=33A008239
- a(n) = floor(binomial(n,3)/3).at n=35A011849
- Numbers k such that the continued fraction for sqrt(k) has period 66.at n=1A020405
- Coordination sequence T6 for Zeolite Code MWW.at n=31A024991
- a(n) = a(1)*a(n-1) + a(2)*a(n-2) + ... + a(n-3)*a(3) for n >= 4, with initial terms 1, 1, 3, 3.at n=10A025256
- Numbers that are the sum of 3 distinct nonzero squares in exactly 9 ways.at n=41A025347
- 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 30.at n=21A031528
- Numbers k such that the period of the continued fraction for sqrt(k) contains exactly 30 ones.at n=4A031798
- Fractional part of square root of a(n) starts with 7: first term of runs.at n=44A034113
- Zeckendorf expansion of n: repeatedly subtract the largest Fibonacci number you can until nothing remains. Big-endian concatenation of decimals.at n=30A035514
- Number of partitions of n with equal number of parts congruent to each of 0 and 3 (mod 5).at n=32A035554
- Position of first term > 2 in n-th row of Gilbreath array shown in A036262.at n=35A036277
- Numbers k such that d(i) is a power of 2 for all k <= i <= k+6, where d(i) = number of divisors of i.at n=33A036540
- Coordination sequence T5 for Zeolite Code ESV.at n=31A038414
- 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=25A039833
- Number of partitions satisfying cn(0,5) = cn(2,5) + cn(3,5).at n=37A039859