6681
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 21
- Digital Root
- 3
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 4
Divisibility
- Divisor Count
- 8
- Divisor Sum
- 9504
- Proper Divisor Sum (Aliquot Sum)
- 2823
- 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
- 4160
- Möbius Function
- -1
- Radical
- 6681
- 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
- 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
- 93
- Smith Number
- no
- Vampire Number
- no
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
Appears in sequences
- 10-gonal (or decagonal) pyramidal numbers: a(n) = n*(n + 1)*(8*n - 5)/6.at n=17A007585
- Pseudoprimes to base 70.at n=31A020198
- a(n) = 1*t(n) + 2*t(n-1) + ... + k*t(n+1-k), where k=floor((n+1)/2) and t(n)=2*n+1 (odd numbers).at n=32A023865
- Number of bracelets (turnover necklaces) of n beads of 2 colors, 5 of them black.at n=33A032279
- Numbers whose base-9 representation has exactly 5 runs.at n=27A043634
- a(n) is the smallest value of m such that A002378(m), the m-th oblong number, contains exactly n 4's.at n=4A048537
- Row sums of triangle in A077526.at n=8A077527
- Minimal k > n such that (4k+3n)(4n+3k) is a square.at n=16A083752
- Triangle, read by rows, of the coefficients of [x^k] in G100234(x)^n such that the row sums are 6^n-1 for n>0, where G100234(x) is the g.f. of A100234.at n=48A100235
- Row sums in A100781.at n=16A100784
- Let T(S,Q) be the sequence obtaining by starting with S and repeatedly reversing the digits and adding Q to get the next term. This is T(1016,5), the first S for which T(S,5) reaches a cycle of length 36.at n=26A118879
- Numbers k such that the k-th triangular number contains only digits {1,2,3}.at n=12A119098
- Variant of triangle A008301, read by rows of 2*n+1 terms, such that the first column is the secant numbers (A000364).at n=22A125053
- Variant of triangle A008301, read by rows of 2*n+1 terms, such that the first column is the secant numbers (A000364).at n=18A125053
- A106486-encodings of combinatorial games equivalent to game {0|1}.at n=29A125997
- a(0)=1; a(1)=2; a(2)=5; a(3)=14; for n>3: a(n) = 8*a(n-1)-20*a(n-2)+16*a(n-3)-a(n-4).at n=8A126566
- Odd integers that do not generate monotonically decreasing infinitary aliquot sequences.at n=15A127667
- a(0)=0. a(n) = a(n-1) + sum of positive integers which are <= n and not part of the sequence.at n=35A129694
- Number of intersection points of all lines through pairs of vertices of a regular n-gon.at n=14A146212
- a(n) = (2*n + 1)*(5*n + 6).at n=25A153127