1561
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 13
- Digital Root
- 4
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 1792
- Proper Divisor Sum (Aliquot Sum)
- 231
- 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
- 1332
- Möbius Function
- 1
- Radical
- 1561
- 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
- 60
- 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
- Number of series-reduced trees with n nodes.at n=19A000014
- a(n) = least m such that if a/b < c/d where a,b,c,d are integers in [0,n], then a/b < k/m < c/d for some integer k.at n=45A001000
- A self-generating sequence: a(1)=1, a(2)=2, a(n+1) chosen so that a(n+1)-a(n-1) is the first number not obtainable as a(j)-a(i) for 1<=i<j<=n.at n=44A001149
- Centered octahedral numbers (crystal ball sequence for cubic lattice).at n=10A001845
- Central polygonal numbers: a(n) = n^2 - n + 1.at n=40A002061
- a(n) = C(n,1) + C(n,2) + C(n,3), or n*(n^2 + 5)/6.at n=21A004006
- Coordination sequence T1 for Zeolite Code AFO.at n=26A008015
- Coordination sequence T4 for Zeolite Code DAC.at n=25A008070
- Coordination sequence T6 for Zeolite Code MFI.at n=25A008169
- Crystal ball sequence for 10-dimensional cubic lattice.at n=3A008421
- Coordination sequence T4 for Zeolite Code DFO.at n=30A009878
- Coordination sequence T1 for Zeolite Code RUT.at n=26A009897
- a(n) = floor( n*(n-1)*(n-2)/23 ).at n=34A011905
- Positive integers n such that 2^n == 2^7 (mod n).at n=44A015927
- Pseudoprimes to base 39.at n=4A020167
- Pseudoprimes to base 40.at n=11A020168
- Strong pseudoprimes to base 39.at n=1A020265
- Strong pseudoprimes to base 40.at n=5A020266
- Numbers k such that the continued fraction for sqrt(k) has period 60.at n=4A020399
- Number of connected regular linearized chord diagrams of degree n.at n=8A022494