7721
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 17
- Digital Root
- 8
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 4
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 8832
- Proper Divisor Sum (Aliquot Sum)
- 1111
- 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
- 6612
- Möbius Function
- 1
- Radical
- 7721
- 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
- yes
- Harshad Number
- no
- Narcissistic Number
- no
- Collatz Steps
- 114
- 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 atoms in a decahedron with n shells.at n=21A004068
- Number of isonemal fabrics of period exactly n.at n=16A005441
- Convolution of Lucas numbers and (1, p(1), p(2), ...).at n=13A023617
- Numbers k not ending in 0 such that for some base b, k_b is the reverse of k_10 (where k_b denotes k written in base b).at n=43A034294
- Denominators of continued fraction convergents to sqrt(308).at n=10A041581
- a(n) = (F(3*n) - 2*F(n))/6, where F=A000045 (the Fibonacci sequence).at n=8A049674
- Beginning with 1, numbers such that the differences a(k)-a(k-1) are distinct and every concatenation n>1 is prime.at n=41A090504
- Numbers n such that p(8n) is prime, where p(n) is the number of partitions of n.at n=20A114168
- Number of partitions of n-1 boys and one girl with no couple.at n=25A120452
- Cube of the Steinbach matrix as a characteristic polynomial triangular array.at n=61A122185
- a(n) is the least exponent e such that 3^e has exactly n consecutive 3's in its decimal representation.at n=7A131550
- G.f. is the polynomial (1-x^3) * (1-x^6) * (1-x^9) * (1-x^12) * (1-x^15) * (1-x^18) * (1-x^21) * (1-x^24) * (1-x^27) * (1-x^30) * (1-x^33) / (1-x)^11.at n=6A162628
- Number of (w,x,y,z) with all terms in {1,...,n} and |w-x|=|x-y|+|y-z|.at n=21A212570
- Sum over all Motzkin paths of length n of products over all peaks p of (x_p+n*y_p)/y_p, where x_p and y_p are the coordinates of peak p.at n=7A266386
- Irregular triangle read by rows: T(n,i) = number of n X n semi-canonical binary matrices with exactly i 1's, where 0 <= i <= n^2.at n=69A268523
- Number of active (ON, black) cells in n-th stage of growth of two-dimensional cellular automaton defined by "Rule 203", based on the 5-celled von Neumann neighborhood.at n=47A270725
- Number of squarefree parts in the partitions of n into 6 parts.at n=39A309458
- Number of nonempty pairwise coprime subsets of {1,...,n}, where a single number is not considered to be pairwise coprime unless it is equal to 1.at n=22A320426
- Number of interior vertices formed by drawing the lines connecting any two of the 2*(n+2) perimeter points of a 3 X (n+1) square grid.at n=12A331767
- Odd composite integers m such that A004187(3*m-J(m,45)) == 7*J(m,45) (mod m) and gcd(m,45)=1, where J(m,45) is the Jacobi symbol.at n=35A340241