1321
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 7
- Digital Root
- 7
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 1
Divisibility
- Divisor Count
- 2
- Divisor Sum
- 1322
- Proper Divisor Sum (Aliquot Sum)
- 1
- 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
- 1320
- Möbius Function
- -1
- Radical
- 1321
- Omega Function (Ω)
- 1
- Little Omega Function (ω)
- 1
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
- 101
- Smith Number
- no
- Vampire Number
- no
Primality
- Prime
- yes
- Composite Number
- no
- Semiprime
- no
- Squarefree Number
- yes
- Prime Power
- yes
- Prime Factorization
- no
- Twin Prime
- yes
- Mersenne Prime
- no
- Sophie Germain Prime
- no
- Safe Prime
- no
- Powerful Number
- no
- Achilles Number
- no
- Prime Index
- 216
- Perfect Power
- no
- Smooth Number
- no
- Carmichael Number
- no
Classification
- Even
- no
- Odd
- yes
Appears in sequences
- Primes p of the form 3k+1 such that sum_{x=1..p} cos(2*Pi*x^3/p) < -sqrt(p).at n=18A000923
- Flavius Josephus's sieve: Start with the natural numbers; at the k-th sieving step, remove every (k+1)-st term of the sequence remaining after the (k-1)-st sieving step; iterate.at n=40A000960
- Squares written in base 4.at n=11A001739
- Largest prime factor of 2^n + 1.at n=30A002587
- Number of partitions of n into parts 5k+2 or 5k+3.at n=57A003106
- Reverse digits of number of partitions of n.at n=34A004089
- Primes written in base 5.at n=46A004679
- Atkinson-Negro-Santoro sequence: a(n+1) = 2*a(n) - a(n-floor(n/2+1)).at n=12A005255
- Primes p such that (p+1)/2 is prime.at n=26A005383
- a(n) = floor(tau*a(n-1)) + a(n-2) with a(0)=0 and a(1)=1.at n=12A005821
- Greater of twin primes.at n=45A006512
- Primes of form 8n+1, that is, primes congruent to 1 mod 8.at n=49A007519
- Integers written in factorial base.at n=47A007623
- Coordination sequence T2 for Zeolite Code AET.at n=25A008008
- Coordination sequence T1 for Zeolite Code AFY.at n=30A008029
- Coordination sequence T4 for Zeolite Code EMT.at n=30A008089
- Coordination sequence T1 for Zeolite Code -CHI.at n=23A009846
- a(n) is prime and sum of all primes <= a(n) is prime.at n=28A013917
- Primes p==1 (mod 6) such that 3 and -3 are both cubes (one implies other) modulo p.at n=32A014753
- 3 and -3 are both 4th powers (one implies other) mod these primes p=1 mod 8.at n=10A014755