7021
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 10
- Digital Root
- 1
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 1
Divisibility
- Divisor Count
- 8
- Divisor Sum
- 8640
- Proper Divisor Sum (Aliquot Sum)
- 1619
- 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
- 5568
- Möbius Function
- -1
- Radical
- 7021
- 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
- yes
- 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
- 44
- 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
- a(2*n) = floor( 17*2^n/14 ), a(2*n+1) = floor( 12*2^n/7 ).at n=25A003143
- Number of nonequivalent dissections of a polygon into n triangles by nonintersecting diagonals rooted at a cell up to rotation and reflection.at n=10A003446
- Number of n-step spirals on hexagonal lattice.at n=11A006776
- Expansion of e.g.f.: exp(x)/cosh(log(1+x)).at n=9A009294
- Numbers k such that the continued fraction for sqrt(k) has period 82.at n=13A020421
- Base-2 digits are, in order, the first n terms of the periodic sequence with initial period [1,1,0].at n=13A033129
- a(n) = (2*n-1)*(4*n-1).at n=30A033567
- Triangular numbers that have some nontrivial permutation of digits which is also triangular.at n=30A034291
- Base-4 digits are, in order, the first n terms of the periodic sequence with initial period 1,2,3.at n=6A037604
- Numbers whose maximal base-8 run length is 4.at n=18A037995
- Numerators of continued fraction convergents to sqrt(908).at n=5A042754
- a(n)=(s(n)+3)/10, where s(n)=n-th base 10 palindrome that starts with 7.at n=24A043086
- Numbers having four 5's in base 8.at n=1A043444
- Smallest value of x such that M(x) = -n, where M(x) is Mertens's function A002321.at n=28A051401
- Inverse Mertens function: smallest k such that |M(k)| = n, where M(x) is Mertens's function A002321.at n=28A051402
- An inverse to Mertens's function: smallest k >= 2 such that Mertens's function |M(k)| (see A002321) is equal to n.at n=29A060434
- Centered 9-gonal (also known as nonagonal or enneagonal) numbers. Every third triangular number, starting with a(1)=1.at n=39A060544
- Numbers k such that k and its reversal are both multiples of 17.at n=24A062906
- Non-palindromic number and its reversal are both multiples of 17.at n=16A062915
- Triangular numbers with sum of digits = 10.at n=19A068129