1021
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 4
- Digital Root
- 4
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 1
Divisibility
- Divisor Count
- 2
- Divisor Sum
- 1022
- 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
- 1020
- Möbius Function
- -1
- Radical
- 1021
- 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
- 49
- 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
- 172
- 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=43A000921
- Primes p such that the multiplicative order of 2 modulo p is (p-1)/3.at n=14A001133
- Numerators of continued fraction convergents to fifth root of 5.at n=9A002364
- Squares written in base 8.at n=22A002441
- Sextan primes: p = (x^6 + y^6)/(x^2 + y^2).at n=7A002647
- Divisible only by primes congruent to 6 mod 7.at n=30A004624
- Primes written in base 4.at n=20A004678
- Primes written in base 6.at n=49A004680
- Fibonacci numbers written in base 3.at n=9A004686
- Smallest prime in class n (sometimes written n+) according to the Erdős-Selfridge classification of primes.at n=4A005113
- Primes p such that 1 + product of primes up to p is prime.at n=8A005234
- Erroneous version of A016054.at n=6A006031
- a(n) = 1 + n/2 + 9*n^2/2.at n=15A006137
- Prime self (or Colombian) numbers: primes not expressible as the sum of an integer and its digit sum.at n=21A006378
- Greater of twin primes.at n=35A006512
- Emirps (primes whose reversal is a different prime).at n=37A006567
- Numbers in base 3.at n=34A007089
- Primes with both 10 and -10 as primitive root.at n=30A007349
- Primes whose reversal in base 10 is also prime (called "palindromic primes" by David Wells, although that name usually refers to A002385). Also called reversible primes.at n=57A007500
- Primes of the form 8k + 5.at n=44A007521