1921
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 13
- Digital Root
- 4
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 2052
- Proper Divisor Sum (Aliquot Sum)
- 131
- 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
- 1792
- Möbius Function
- 1
- Radical
- 1921
- 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
- 143
- Smith Number
- yes
- 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
- Pentanacci numbers: a(n) = a(n-1) + a(n-2) + a(n-3) + a(n-4) + a(n-5) with a(0) = a(1) = a(2) = a(3) = a(4) = 1.at n=14A000322
- a(n) = 8*a(n-1) - a(n-2); a(0) = 1, a(1) = 4.at n=4A001091
- Numbers that are the sum of 2 positive 4th powers.at n=19A003336
- Number of nonequivalent dissections of an n-gon into 3 polygons by nonintersecting diagonals up to rotation and reflection.at n=32A003453
- Sums of distinct nonzero 4th powers.at n=47A003999
- "Magic" integers: a(n+1) is the smallest integer m such that there is no overlap between the sets {m, m-a(i), m+a(i): 1 <= i <= n} and {a(i), a(i)-a(j), a(i)+a(j): 1 <= j < i <= n}.at n=27A004210
- Numbers that are the sum of at most 2 nonzero 4th powers.at n=26A004831
- Multilevel sieve: at k-th step, accept k numbers, reject k, accept k, ...at n=8A005209
- a(n) = 2*a(n-1)^2 - 1, a(0) = 4, a(1) = 31.at n=2A005828
- Numbers n such that n! has a square number of digits.at n=34A006488
- Nonnegative integers n such that n^2*(n+1)*(2*n+1)^2*(7*n+1)/36 is a square.at n=6A007750
- Even bisection of A007750.at n=3A007751
- Coordination sequence T3 for Zeolite Code MTT.at n=27A008191
- Coordination sequence T2 for Moganite, also for BGB1.at n=28A008259
- 4-dimensional centered cube numbers.at n=5A008514
- For any circular arrangement of 0..n-1, let S be the sum of cubes of every sum of two contiguous numbers; then a(n) is the number of distinct values of S.at n=10A008781
- Coordination sequence for MgNi2, Position Mg2.at n=11A009935
- Pseudoprimes to base 15.at n=9A020143
- Pseudoprimes to base 18.at n=19A020146
- Pseudoprimes to base 35.at n=11A020163