181
domain: N
Properties
Digital Properties
- Digit Count
- 3
- Digit Sum
- 10
- Digital Root
- 1
- Palindromic Number
- yes
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 1
Divisibility
- Divisor Count
- 2
- Divisor Sum
- 182
- 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
- 180
- Möbius Function
- -1
- Radical
- 181
- 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
- 18
- 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
- 42
- Perfect Power
- no
- Smooth Number
- no
- Carmichael Number
- no
Classification
- Even
- no
- Odd
- yes
Names
- German
- einshunderteinundachtzig· ordinal: einshunderteinundachtzigste
- English
- one hundred eighty-one· ordinal: one hundred eighty-first
- Spanish
- ciento ochenta y uno· ordinal: 181º
- French
- cent quatre-vingt-un· ordinal: cent quatre-vingt-unième
- Italian
- centoottantuno· ordinal: 181º
- Latin
- centum octoginta unus· ordinal: 181.
- Portuguese
- cento e oitenta e um· ordinal: 181º
Appears in sequences
- Number of centered hydrocarbons with n atoms.at n=12A000022
- Number of positive integers <= 2^n of the form 3*x^2 + 4*y^2.at n=10A000049
- Local stops on New York City 1 Train (Broadway-7 Avenue Local) subway.at n=21A000053
- Local stops on New York City A line subway.at n=21A000054
- a(n) = floor(n^(3/2)).at n=32A000093
- Positive zeros of Bessel function of order 0 rounded to nearest integer.at n=57A000134
- a(n) = n*a(n-1) + (n-2)*a(n-2), with a(0) = 0, a(1) = 1.at n=5A000153
- Even sequences with period 2n.at n=7A000206
- Tetranacci numbers: a(n) = a(n-1) + a(n-2) + a(n-3) + a(n-4) with a(0) = a(1) = a(2) = a(3) = 1.at n=10A000288
- Number of bipartite partitions of n white objects and 2 black ones.at n=8A000291
- Numbers that are the sum of 2 but no fewer nonzero squares.at n=59A000415
- Primes and squares of primes.at n=47A000430
- Number of steps to reach 1 in sequence A000546.at n=26A000547
- n-th superior highly composite number A002201(n) is product of first n terms of this sequence.at n=64A000705
- Strobogrammatic numbers: the same upside down.at n=9A000787
- Total number of 1's in binary expansions of 0, ..., n.at n=61A000788
- Primes p of the form 3k+1 such that Sum_{x=1..p} cos(2*Pi*x^3/p) > sqrt(p).at n=9A000921
- Genus of complete graph on n nodes.at n=49A000933
- 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=14A000960
- Powers of primes. Alternatively, 1 and the prime powers (p^k, p prime, k >= 1).at n=56A000961