8121
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 12
- Digital Root
- 3
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 10832
- Proper Divisor Sum (Aliquot Sum)
- 2711
- 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
- 5412
- Möbius Function
- 1
- Radical
- 8121
- 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
- 39
- 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 Barlow packings with group P6(bar)m2 that repeat after 2n layers.at n=14A011949
- Number of ordered triples of integers from [ 1..n ] with no global factor.at n=37A015631
- a(n) = least m such that if r and s in {1/2, 1/4, 1/6, ..., 1/2n} satisfy r < s, then r < k/m < (k+4)/m < s for some integer k.at n=29A024848
- 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 60.at n=22A031558
- Decimal part of cube root of a(n) starts with 1: first term of runs.at n=18A034127
- Positive numbers having the same set of digits in base 4 and base 9.at n=42A037427
- a(n)^3 is smallest cube containing exactly n 5's.at n=6A048370
- Numbers whose cubes contain more than half the same digit and do not end in 0.at n=22A060814
- Geometric mean of the digits = 2. In other words, the product of the digits is = 2^k where k is the number of digits.at n=43A061426
- Partial sums of sequence (essentially A002378): 1, 2, 6, 12, 20, 30, 42, 56, 72, 90, ...at n=28A064999
- Numbers, not composed of the same digits, such that the geometric and arithmetic means of their decimal digits are integers.at n=32A067452
- Centered 20-gonal (or icosagonal) numbers.at n=28A069133
- Fundamental discriminants of real quadratic number fields with class number 5.at n=38A094614
- Number of distinct products i*j*k*l for 1 <= i < j < k < l <= n.at n=31A100438
- Shadow of sqrt(2).at n=44A110557
- Greatest n-bit number whose binary representation's substrings represent the maximal number (A112509(n)) of distinct integers.at n=12A112511
- Triangle, read by rows, such that T(n,k) = T(n-1,k-1) + [T^2](n-2,k-1) with T(n,0) = T(n,n) = 1 for n>=0, k>=0.at n=57A113983
- Column 2 of triangle A113983; also a(n) = A113983(n+1,1) + [A113983^2](n,1).at n=8A113985
- 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, 0, 0), (0, -1, 1), (1, -1, 0), (1, 0, -1), (1, 1, 0)}.at n=8A149334
- Numbers k such that d(i)|(k - i) for i = 1..p where d(1), d(2), ..., d(p) are the digits of the decimal expansion of k.at n=70A177902