2021
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 5
- Digital Root
- 5
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 1
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 2112
- Proper Divisor Sum (Aliquot Sum)
- 91
- 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
- 1932
- Möbius Function
- 1
- Radical
- 2021
- 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
- 63
- 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
- Primes in ternary.at n=17A001363
- a(n) = (6*n+1)*(6*n+5).at n=7A001513
- a(n) = n concatenated with n + 1.at n=19A001704
- Numbers k such that (k^2 + k + 1)/19 is prime.at n=45A002643
- Primes written in base 4.at n=32A004678
- a(n) = ceiling(n*phi^8), where phi is the golden ratio, A001622.at n=43A004963
- Number of 4-valent labeled graphs with n nodes where multiple edges and loops are allowed.at n=5A005816
- Products of 2 successive primes.at n=13A006094
- Coordination sequence T5 for Zeolite Code MFS.at n=28A008177
- Coordination sequence T1 for Zeolite Code MTN.at n=27A008186
- "Pascal sweep" for k=9: draw a horizontal line through the 1 at C(k,0) in Pascal's triangle; rotate this line and record the sum of the numbers on it (excluding the initial 1).at n=34A009540
- Coordination sequence T1 for Zeolite Code RTH.at n=31A009893
- Coefficients in expansion of Pi as Sum_{n>=1} a(n)/(n*n!*(n+1)!), as found by greedy algorithm.at n=47A011191
- Numbers n such that phi(n) * sigma(n) + 16 is a perfect square.at n=38A015729
- Powers of sqrt(21) rounded to nearest integer.at n=5A017968
- Powers of sqrt(21) rounded up.at n=5A017969
- Powers of fourth root of 21 rounded to nearest integer.at n=10A018106
- Powers of fourth root of 21 rounded up.at n=10A018107
- Number of partitions of 1/n into 4 reciprocals of positive integers.at n=6A020327
- n written in fractional base 4/2.at n=21A024630