1981
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 19
- Digital Root
- 1
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 3
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 2272
- Proper Divisor Sum (Aliquot Sum)
- 291
- 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
- 1692
- Möbius Function
- 1
- Radical
- 1981
- 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
- 99
- 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
- Expansion of 1/((1-x)^2*(1-x^2)*(1-x^3)).at n=38A000601
- Numbers k such that (1,k) is "good".at n=22A000696
- Central polygonal numbers: a(n) = n^2 - n + 1.at n=45A002061
- a(n) = 2^n - 1 - n*(n+1)/2.at n=11A002662
- Numbers k such that k, k+1 and k+2 have the same number of divisors.at n=37A005238
- Number of n X 4 binary matrices under row and column permutations and column complementations.at n=8A006382
- Number of connected regular bipartite graphs of degree 5 with 2n nodes.at n=4A006825
- G.f.: Product_{k>=1} (1 + x^(2*k - 1)) / (1 - x^(2*k)).at n=34A006950
- Triangle read by rows: T(n,k) is the number of simple regular connected bipartite graphs with 2n nodes and degree k, (2 <= k <= n).at n=31A008326
- Triangle read by rows: T(n,k) is the number of simple regular bipartite graphs with 2n nodes and degree k, (0 <= k <= n).at n=49A008327
- Triangle read by rows: T(n,k) is the number of simple regular bipartite graphs with 2n nodes and degree k, (0 <= k <= n).at n=50A008327
- a(n) = (n+1)*(n^2 +8*n +6)/6. Number of n-dimensional partitions of 4. Number of terms in 4th derivative of a function composed with itself n times.at n=20A008778
- a(n) = Sum_{k=0..8} binomial(n,k).at n=11A008861
- Triangle read by rows of partial sums of binomial coefficients: T(n,k) = Sum_{i=0..k} binomial(n,i) (0 <= k <= n); also dimensions of Reed-Muller codes.at n=74A008949
- Number of 5-tuples of different integers from [ 1,n ] with no global factor.at n=13A015640
- Positive integers n such that 2^n == 2^7 (mod n).at n=49A015927
- Pseudoprimes to base 44.at n=23A020172
- Pseudoprimes to base 45.at n=19A020173
- Strong pseudoprimes to base 44.at n=7A020270
- Strong pseudoprimes to base 45.at n=2A020271