161
domain: N
Properties
Digital Properties
- Digit Count
- 3
- Digit Sum
- 8
- Digital Root
- 8
- Palindromic Number
- yes
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 1
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 192
- Proper Divisor Sum (Aliquot Sum)
- 31
- 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
- 132
- Möbius Function
- 1
- Radical
- 161
- Omega Function (Ω)
- 2
- Little Omega Function (ω)
- 2
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
- 98
- Smith Number
- no
Primality
- Prime
- no
- Composite Number
- yes
- Semiprime
- yes
- Squarefree Number
- yes
- Prime Power
- no
- Prime Factorization
- no
- Twin Prime
- no
- Mersenne Prime
- no
- Sophie Germain Prime
- no
- Safe Prime
- no
- Powerful Number
- no
- Achilles Number
- no
- Perfect Power
- no
- Smooth Number
- no
- Carmichael Number
- no
Classification
- Even
- no
- Odd
- yes
Names
- German
- einshunderteinundsechzig· ordinal: einshunderteinundsechzigste
- English
- one hundred sixty-one· ordinal: one hundred sixty-first
- Spanish
- ciento sesenta y uno· ordinal: 161º
- French
- cent soixante et un· ordinal: cent soixante et unième
- Italian
- centosessantuno· ordinal: 161º
- Latin
- centum sexaginta unus· ordinal: 161.
- Portuguese
- cento e sessenta e um· ordinal: 161º
Appears in sequences
- Number of integers <= 2^n of form x^2 - 2y^2.at n=9A000047
- Number of trees of diameter 4.at n=15A000094
- a(n) = floor(n^2/3).at n=22A000212
- Let A(n) = #{(i,j,k): i^2 + j^2 + k^2 <= n}, V(n) = (4/3)Pi*n^(3/2), P(n) = A(n) - V(n); A000092 gives values of n where |P(n)| sets a new record; sequence gives (nearest integer to, I believe) P(A000092(n)).at n=14A000223
- Hexanacci numbers with a(0) = ... = a(5) = 1.at n=11A000383
- n! never ends in this many 0's.at n=31A000966
- Numerators of continued fraction convergents to sqrt(5).at n=4A001077
- Generalized octagonal numbers: k*(3*k-2), k=0, +- 1, +- 2, +-3, ...at n=14A001082
- Simple continued fraction expansion of Pi.at n=79A001203
- Semiprimes (or biprimes): products of two primes.at n=53A001358
- a(n) is the number of partitions of n into at most 3 parts; also partitions of n+3 in which the greatest part is 3; also number of unlabeled multigraphs with 3 nodes and n edges.at n=41A001399
- Nearest integer to 2*n*log(n).at n=25A001618
- Sorting numbers: number of comparisons for merge insertion sort of n elements.at n=39A001768
- Triangular numbers plus quarter-squares: n*(n+1)/2 + floor((n+1)^2/4) (i.e., A000217(n) + A002620(n+1)).at n=14A001859
- v-pile positions of the 4-Wythoff game with i=3.at n=30A001968
- Cullen numbers: a(n) = n*2^n + 1.at n=5A002064
- Palindromes in base 10.at n=25A002113
- Numbers k for which the rank of the elliptic curve y^2 = x^3 + k is 2.at n=20A002155
- Numbers k for which the rank of the elliptic curve y^2 = x^3 + k*x is 0.at n=71A002158
- Least number k such that phi(k) = m, where m runs through the values (A002202) taken by phi.at n=49A002181