7209
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 18
- Digital Root
- 9
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 1
Divisibility
- Divisor Count
- 10
- Divisor Sum
- 10890
- Proper Divisor Sum (Aliquot Sum)
- 3681
- 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
- 4752
- Möbius Function
- 0
- Radical
- 267
- Omega Function (Ω)
- 5
- 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
- 70
- Smith Number
- no
- Vampire Number
- no
Primality
- Prime
- no
- Composite Number
- yes
- Semiprime
- no
- Squarefree Number
- no
- 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(n) = (10n+1)*(10n+9).at n=8A001535
- Odd heptagonal numbers (A000566).at n=27A014637
- Numbers k such that the continued fraction for sqrt(k) has period 84.at n=17A020423
- Dying rabbits: a(n) = a(n-1) + a(n-2) - a(n-7).at n=21A023437
- Iterate the map in A006368 starting at 8.at n=51A028393
- Numbers k such that the period of the continued fraction for sqrt(k) contains exactly 48 ones.at n=17A031816
- Numbers k such that k^4 can be written as a sum of four positive 4th powers with no common factor.at n=20A039664
- Numbers having three 0's in base 9.at n=31A043455
- Ordered factorizations with one level of parentheses indexed by prime signatures. A050354(A025487).at n=26A050355
- Number of fibered rational knots with n crossings.at n=21A051449
- Numbers which yield a prime whenever a 1 is inserted anywhere in them (including at the beginning or end).at n=58A068679
- Row sums of the triangle described in A082200.at n=20A082203
- Main diagonal of A101858.at n=44A101863
- Numbers of planar triangulations with minimum degree 5 and without separating 3-cycles - that is 3-cycles where the interior and exterior contain at least one vertex.at n=12A111357
- a(0)=1, a(1)=1, a(n) = 9*a(n/2) for even n >= 2, and a(n) = 8*a((n-1)/2) + a((n+1)/2) for odd n >= 3.at n=20A116526
- Heptagonal numbers for which the sum of the digits is also a heptagonal number.at n=13A117650
- Heptagonal numbers A000566 which are the sum of two other heptagonal numbers > 0.at n=4A133251
- Sequence of a(n) such that : define p(0)=2 the first prime, then p(n+1)=least prime p of the form a(n)*p(n)*(a(n)*p(n)+1)-1 with a twin prime p+2.at n=5A143181
- Second bisection of A061041: a(n) = A061041(2n+1) = (2*n+1)*(2*n+9).at n=40A145923
- Number of n X n binary arrays symmetric under 90 degree rotation with all ones connected only in a 1001-1111-1001 pattern in any orientation.at n=17A146931