861
domain: N
Properties
Digital Properties
- Digit Count
- 3
- Digit Sum
- 15
- Digital Root
- 6
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 3
Divisibility
- Divisor Count
- 8
- Divisor Sum
- 1344
- Proper Divisor Sum (Aliquot Sum)
- 483
- 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
- 480
- Möbius Function
- -1
- Radical
- 861
- Omega Function (Ω)
- 3
- Little Omega Function (ω)
- 3
Special
- Factorial
- no
- Catalan Number
- no
- Bell Number
- no
- Motzkin Number
- no
- Primorial
- no
Figurate Numbers
- Fibonacci Number
- no
- Triangular Number
- yes
- Perfect Square
- no
- Perfect Cube
- no
- Pentagonal Number
- no
- Hexagonal Number
- yes
- 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
- 103
- Smith Number
- yes
Primality
- Prime
- no
- Composite Number
- yes
- Semiprime
- no
- 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
- achthunderteinundsechzig· ordinal: achthunderteinundsechzigste
- English
- eight hundred sixty-one· ordinal: eight hundred sixty-first
- Spanish
- ochocientos sesenta y uno· ordinal: 861º
- French
- huit cent soixante et un· ordinal: huit cent soixante et unième
- Italian
- ottocentosessantuno· ordinal: 861º
- Latin
- octingenti sexaginta unus· ordinal: 861.
- Portuguese
- oitocentos e sessenta e um· ordinal: 861º
Appears in sequences
- Hexagonal numbers: a(n) = n*(2*n-1).at n=21A000384
- Number of compositions of n into 3 ordered relatively prime parts.at n=42A000741
- MacMahon's solid partitions of n in which 3 is the smallest summand.at n=8A002044
- a(n) = a(n-1) + a(n-2) - a(n-3).at n=33A002798
- Numbers that are the sum of 11 positive 5th powers.at n=37A003356
- Numbers that are the sum of 7 positive 6th powers.at n=10A003363
- Binomial coefficient C(3n,n-12).at n=2A004330
- Binomial coefficient C(6n,n-5).at n=2A004360
- Binomial coefficient C(7n,n-4).at n=2A004372
- a(n) = floor(Fibonacci(n)/3).at n=18A004696
- a(n) = round(n*phi^10), where phi is the golden ratio, A001622.at n=7A004945
- a(n) = ceiling(n*phi^10), where phi is the golden ratio, A001622.at n=7A004965
- Smith (or joke) numbers: composite numbers k such that sum of digits of k = sum of digits of prime factors of k (counted with multiplicity).at n=42A006753
- a(n) = n OR n^2 (applied to binary expansions).at n=28A007745
- Number of conjugacy classes of compact Cartan subgroups in Sp_{2n}(F), where p>n and the p-adic field F contains all r-th roots of unity for all r <= 2n.at n=3A007793
- Coordination sequence T2 for Zeolite Code ATT.at n=21A008042
- Coordination sequence T3 for Zeolite Code HEU.at n=19A008118
- Expansion of Jacobi theta constant theta_2^6 /(64q^(3/2)).at n=20A008440
- Multiples of 21.at n=41A008603
- A B_2 sequence: a(n) = least value such that the sequence increases and pairwise sums of distinct terms are all distinct.at n=26A010672