7981
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 25
- Digital Root
- 7
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 8352
- Proper Divisor Sum (Aliquot Sum)
- 371
- 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
- 7612
- Möbius Function
- 1
- Radical
- 7981
- 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
- 52
- 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
- Numbers k such that the period of the continued fraction for sqrt(k) contains exactly 78 ones.at n=2A031846
- a(n) = n^3 - n + 1.at n=20A061600
- Nested floor product of n and fractions (k+1)/k for all k>0 (mod 3), divided by 3.at n=38A073360
- The last number for which a determinant of base-n numbers is nonzero.at n=18A079505
- a(n) = 10*n^2 + 5*n + 1.at n=28A080860
- Composite numbers k such that the continued fraction for k/m contains no 2 for any 1 <= m <= k.at n=28A082409
- Antidiagonal sums of table A083362.at n=24A083364
- Matrix product of unsigned Lah-triangle |A008297(n,k)| and Stirling2-triangle A008277(n,k).at n=16A088814
- Numbers k such that 13k = 6j^2 + 6j + 1.at n=20A106390
- Numbers k such that the square of k is the concatenation of two numbers m and m-8.at n=2A115446
- Invariant number of polygons of n-circum-C_5 H_5 systems.at n=8A122678
- Number of Delta<=6 Berge perfect graphs on n nodes.at n=7A123417
- Number of ways to build a contiguous building with n LEGO blocks of size 5 X 5 on top of a fixed block of the same size.at n=1A123847
- a(1) = 1; a(n) = max{ 5*a(k) + a(n-k) | 1 <= k <= n/2 } for n > 1.at n=36A130667
- a(n) is the number of n-cell polyiamonds (triangular polyominoes) with perimeter n+2.at n=12A131481
- Trajectory of 6 under iteration of the map k -> A087712(k).at n=21A144760
- Trajectory of 10 under iteration of the map k -> A087712(k).at n=23A144814
- Number of walks within N^3 (the first octant of Z^3) starting at (0,0,0) and consisting of n steps taken from {(-1, -1, 1), (-1, 1, 0), (0, 0, 1), (0, 1, 0), (1, 0, -1)}.at n=8A149894
- a(n) = 5*n^2 + 20*n + 1.at n=38A162316
- Composite numbers such that exactly ten distinct permutations of digits are prime.at n=23A163562