7123
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
- 7560
- Proper Divisor Sum (Aliquot Sum)
- 437
- 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
- 6688
- Möbius Function
- 1
- Radical
- 7123
- 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
- 49
- 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 unlabeled nonseparable (or 2-connected) graphs (or blocks) with n nodes.at n=7A002218
- Numbers k such that the continued fraction for sqrt(k) has even period and if the last term of the periodic part is deleted the central term is 83.at n=22A031581
- a(n)=Sum{a(k): k=0,1,2,...,n-3,n-1}; a(n-2) is not a summand; 2 initial terms required.at n=16A049854
- a(n) = floor(A*a(n-1) + B*a(n-2) + C)/p^r, where p^r is the highest power of p dividing floor(A*a(n-1) + B*a(n-2) + C), A=1.0001, B=1.0001, C=1, p=2.at n=30A053521
- Open 3-dimensional ball numbers (version 1): a(n) is the number of integer points (i,j,k) contained in an open ball of diameter n, centered at (0,0,0).at n=24A053592
- a(n) = A064842(n)/2.at n=34A064843
- Semiprimes p1*p2 such that p2 > p1 and p2 mod p1 = 11.at n=24A064909
- Numbers k such that sigma(k) divides sigma(phi(k)).at n=30A066831
- Numbers n such that sigma(phi(n))/sigma(n) = 2.at n=20A067382
- Number of solutions to x^2 + y^2 + z^2 < n^2; number of lattice points inside a sphere of radius n.at n=12A078183
- a(1)=4, then least semiprime > a(n-1) such that when all in the sequence are concatenated together they form a prime.at n=25A085703
- a(n) is the smallest number greater than a(n-1) such that in a(0) through a(n) no digit occurs more than once more than any other digit.at n=28A095204
- Number of squares on infinite half chessboard at <=n knight moves from a fixed point on the diagonal.at n=32A098499
- Numbers k such that k and 8*k, taken together, are zeroless pandigital.at n=19A115932
- Where record values of A119999 occur.at n=28A120001
- Largest number not the sum of n distinct nonzero squares.at n=21A129210
- Number of n X n binary arrays symmetric under 90-degree rotation with all ones connected only in a 1 X 5 or 5 X 1 block.at n=14A145970
- Number of ways that a 1 X n rectangular tile T, marked into n unit squares, can be surrounded by one layer of copies of itself laid in the plane grid generated by the units of T. Ways that differ by rotation or reflection are not counted as different. The surrounded tile is the exact surrounded region.at n=11A159294
- a(n) is the smallest number not yet in the sequence such that the concatenation of all terms yields a periodic stream of digits 1, 2, 3, ..., 7 (repeat from 1).at n=26A165305
- Nonhomogeneous three-term sequence a(n) = a(n-1) + a(n-2) + n.at n=15A179991