2561
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 14
- Digital Root
- 5
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 2772
- Proper Divisor Sum (Aliquot Sum)
- 211
- 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
- 2352
- Möbius Function
- 1
- Radical
- 2561
- 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
- 146
- Smith Number
- no
- Vampire 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
Appears in sequences
- a(n) = Sum_{k = 1..n} floor(2^k / k).at n=13A000801
- Number of bipartite partitions.at n=11A002768
- Numbers that are the sum of 11 positive 8th powers.at n=10A003389
- Numbers that are the sum of 6 positive 9th powers.at n=5A003395
- a(n) = n*(7*n^2 - 1)/6.at n=13A004126
- Numbers that are the sum of at most 6 positive 9th powers.at n=26A004890
- Numbers that are the sum of at most 7 positive 9th powers.at n=31A004891
- Numbers that are the sum of at most 8 positive 9th powers.at n=36A004892
- Numbers that are the sum of at most 9 positive 9th powers.at n=41A004893
- Reve's puzzle: number of moves needed to solve the Towers of Hanoi puzzle with 4 pegs and n disks, according to the Frame-Stewart algorithm.at n=39A007664
- Coordination sequence T2 for Zeolite Code APC.at n=35A008033
- Coordination sequence T1 for Zeolite Code LAU.at n=36A008124
- Coordination sequence T8 for Zeolite Code MFI.at n=32A008171
- Coordination sequence for sigma-CrFe, Position Xb.at n=13A009960
- Pseudoprimes to base 14.at n=16A020142
- Numbers k such that the continued fraction for sqrt(k) has period 27.at n=10A020366
- Expansion of 1/((1-x)*(1-2*x)^4).at n=5A027608
- Numbers k such that the continued fraction for sqrt(k) has odd period and if the last term of the periodic part is deleted then there are a pair of central terms both equal to 3.at n=35A031416
- Fractional part of square root of a(n) starts with 6: first term of runs.at n=48A034112
- a(n) = floor(E_(n+1)/E_(n)) where E_n is n-th Euler number (see A028296 and A000364).at n=38A034971