281
domain: N
Properties
Digital Properties
- Digit Count
- 3
- Digit Sum
- 11
- Digital Root
- 2
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 2
- Divisor Sum
- 282
- 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
- 280
- Möbius Function
- -1
- Radical
- 281
- 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
- 42
- 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
- yes
- Safe Prime
- no
- Powerful Number
- no
- Achilles Number
- no
- Prime Index
- 60
- Perfect Power
- no
- Smooth Number
- no
- Carmichael Number
- no
Classification
- Even
- no
- Odd
- yes
Names
- German
- zweihunderteinundachtzig· ordinal: zweihunderteinundachtzigste
- English
- two hundred eighty-one· ordinal: two hundred eighty-first
- Spanish
- doscientos ochenta y uno· ordinal: 281º
- French
- deux cent quatre-vingt-un· ordinal: deux cent quatre-vingt-unième
- Italian
- duecentoottantuno· ordinal: 281º
- Latin
- ducenti octoginta unus· ordinal: 281.
- Portuguese
- duzentos e oitenta e um· ordinal: 281º
Appears in sequences
- a(n) = floor(n^(3/2)).at n=43A000093
- Union of all numbers {p, q} where p and q are both primes or powers of primes and q = p+2.at n=52A001092
- Twin primes.at n=35A001097
- Primes with 3 as smallest primitive root.at n=13A001123
- Primes == +-1 (mod 8).at n=27A001132
- Primes p such that the multiplicative order of 2 modulo p is (p-1)/4.at n=1A001134
- Irregular table read by rows: row n lists prime factors of 10^n + 1, with multiplicity.at n=37A001271
- Lesser of twin primes.at n=18A001359
- Smallest primitive prime factor of Fibonacci number F(n), or 1 if F(n) has no primitive prime factor.at n=27A001578
- Artiads: the primes p == 1 (mod 5) for which Fibonacci((p-1)/5) is divisible by p.at n=1A001583
- Numbers k such that phi(k+2) = phi(k) + 2.at n=30A001838
- v-pile positions of the 4-Wythoff game with i=3.at n=53A001968
- Pythagorean primes: primes of the form 4*k + 1.at n=27A002144
- Numbers k for which the rank of the elliptic curve y^2 = x^3 + k is 2.at n=42A002155
- Smallest primitive factor of 2^(2n+1) + 1.at n=17A002185
- Primitive roots that go with the primes in A002230.at n=31A002229
- 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=28A002313
- Expansion of a modular function for Gamma_0(14).at n=10A002509
- a(n) = Sum_{d|n, d <= 4} d^2 + 4*Sum_{d|n, d>4} d.at n=45A002791
- For n > 4, a(n) is the least integer > a(n-1) with precisely two representations a(n) = a(i) + a(j), 1 <= i < j < n; and a(n) = n for n=1..4.at n=54A003044