521
domain: N
Properties
Digital Properties
- Digit Count
- 3
- Digit Sum
- 8
- Digital Root
- 8
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 2
- Divisor Sum
- 522
- 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
- 520
- Möbius Function
- -1
- Radical
- 521
- 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
- yes
- Tetrahedral Number
- no
- Pell Number
- no
- Tribonacci Number
- no
- Pronic Number
- no
Recreational
- Happy Number
- no
- Harshad Number
- no
- Narcissistic Number
- no
- Collatz Steps
- 123
- Smith 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
- 98
- Perfect Power
- no
- Smooth Number
- no
- Carmichael Number
- no
Classification
- Even
- no
- Odd
- yes
Names
- German
- fünfhunderteinundzwanzig· ordinal: fünfhunderteinundzwanzigste
- English
- five hundred twenty-one· ordinal: five hundred twenty-first
- Spanish
- quinientos veintiuno· ordinal: 521º
- French
- cinq cent vingt et un· ordinal: cinq cent vingt et unième
- Italian
- cinquecentoventuno· ordinal: 521º
- Latin
- quingenti viginti unus· ordinal: 521.
- Portuguese
- quinhentos e vinte e um· ordinal: 521º
Appears in sequences
- Mersenne exponents: primes p such that 2^p - 1 is prime. Then 2^p - 1 is called a Mersenne prime.at n=12A000043
- Lucas numbers (beginning with 1): L(n) = L(n-1) + L(n-2) with L(1) = 1, L(2) = 3.at n=12A000204
- Twin primes.at n=47A001097
- Primes with 3 as smallest primitive root.at n=21A001123
- Primes == +-1 (mod 8).at n=46A001132
- Degrees of primitive irreducible trinomials: n such that 2^n - 1 is a Mersenne prime and x^n + x^k + 1 is a primitive irreducible polynomial over GF(2) for some k with 0 < k < n.at n=8A001153
- Associated Mersenne numbers.at n=13A001350
- Lesser of twin primes.at n=24A001359
- Partial sums of A001462; also a(n) is the last occurrence of n in A001462.at n=56A001463
- Smallest primitive prime factor of Fibonacci number F(n), or 1 if F(n) has no primitive prime factor.at n=25A001578
- Artiads: the primes p == 1 (mod 5) for which Fibonacci((p-1)/5) is divisible by p.at n=4A001583
- A Fielder sequence: a(n) = a(n-1) + a(n-3) + a(n-4), n >= 4.at n=13A001638
- Numbers k such that phi(k+2) = phi(k) + 2.at n=39A001838
- Primes p such that the congruence 2^x = 5 (mod p) is solvable.at n=53A001916
- Number of partitions of floor(5n/2) into n nonnegative integers each no more than 5.at n=15A001975
- Pythagorean primes: primes of the form 4*k + 1.at n=45A002144
- Primes congruent to 1 or 2 modulo 4; or, primes of form x^2 + y^2; or, -1 is a square mod p.at n=46A002313
- Quintan primes: p = (x^5 + y^5)/(x + y).at n=5A002650
- Bisection of Lucas sequence: a(n) = L(2*n+1).at n=6A002878
- Number of coprime chains with largest member n.at n=52A003139