191
domain: N
Properties
Digital Properties
- Digit Count
- 3
- Digit Sum
- 11
- Digital Root
- 2
- Palindromic Number
- yes
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 1
Divisibility
- Divisor Count
- 2
- Divisor Sum
- 192
- 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
- 190
- Möbius Function
- -1
- Radical
- 191
- 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
- 44
- 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
- 43
- Perfect Power
- no
- Smooth Number
- no
- Carmichael Number
- no
Classification
- Even
- no
- Odd
- yes
Names
- German
- einshunderteinundneunzig· ordinal: einshunderteinundneunzigste
- English
- one hundred ninety-one· ordinal: one hundred ninety-first
- Spanish
- ciento noventa y uno· ordinal: 191º
- French
- cent quatre-vingt-onze· ordinal: cent quatre-vingt-onzième
- Italian
- centonovantuno· ordinal: 191º
- Latin
- centum nonaginta unus· ordinal: 191.
- Portuguese
- cento e noventa e um· ordinal: 191º
Appears in sequences
- Local stops on New York City 1 Train (Broadway-7 Avenue Local) subway.at n=22A000053
- Central polygonal numbers (the Lazy Caterer's sequence): n(n+1)/2 + 1; or, maximal number of pieces formed when slicing a pancake with n cuts.at n=19A000124
- Primes p == 3, 9, 11 (mod 20) such that 2p+1 is also prime.at n=7A000355
- Topswops (1): start by shuffling n cards labeled 1..n. If top card is m, reverse order of top m cards, then repeat. a(n) is the maximal number of steps before top card is 1.at n=17A000375
- Topswops (2): start by shuffling n cards labeled 1..n. If the top card is m, reverse the order of the top m cards. Repeat until 1 gets to the top, then stop. Suppose the whole deck is now sorted (if not, discard this case). a(n) is the maximal number of steps before 1 got to the top.at n=17A000376
- Primes and squares of primes.at n=48A000430
- n-th superior highly composite number A002201(n) is product of first n terms of this sequence.at n=65A000705
- Number of disconnected graphs with n nodes.at n=7A000719
- Number of free planar polyenoids with 2n nodes and symmetry point group C_{2h}.at n=6A000935
- Powers of primes. Alternatively, 1 and the prime powers (p^k, p prime, k >= 1).at n=57A000961
- Wagstaff numbers: numbers k such that (2^k + 1)/3 is prime.at n=15A000978
- Numbers k such that sum of squares of k consecutive integers >= 1 is a square.at n=23A001032
- Union of all numbers {p, q} where p and q are both primes or powers of primes and q = p+2.at n=41A001092
- Twin primes.at n=25A001097
- Primes == +-1 (mod 8).at n=17A001132
- Lesser of twin primes.at n=13A001359
- Number of n-node trees of height at most 4.at n=9A001384
- A generalized Fibonacci sequence.at n=31A001584
- Tetranacci numbers A073817 without the leading term 4.at n=7A001648
- Numbers k such that phi(k+2) = phi(k) + 2.at n=23A001838