6991
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
- 4
Divisibility
- Divisor Count
- 2
- Divisor Sum
- 6992
- Proper Divisor Sum (Aliquot Sum)
- 1
- 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
- 6990
- Möbius Function
- -1
- Radical
- 6991
- Omega Function (Ω)
- 1
- Little Omega Function (ω)
- 1
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
- 57
- Smith Number
- no
- Vampire Number
- no
Primality
- Prime
- yes
- Composite Number
- no
- Semiprime
- no
- Squarefree Number
- yes
- Prime Power
- yes
- Prime Factorization
- no
- Twin Prime
- no
- Mersenne Prime
- no
- Sophie Germain Prime
- no
- Safe Prime
- no
- Powerful Number
- no
- Achilles Number
- no
- Prime Index
- 899
- Perfect Power
- no
- Smooth Number
- no
- Carmichael Number
- no
Classification
- Even
- no
- Odd
- yes
Appears in sequences
- T(n, 2*n-4), T given by A027960.at n=18A027966
- 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=12A031581
- Numbers k such that the period of the continued fraction for sqrt(k) contains exactly 54 ones.at n=13A031822
- Numbers whose set of base-15 digits is {1,2}.at n=22A032935
- Numerators of continued fraction convergents to sqrt(885).at n=4A042710
- a(n)=T(2n-1,n), array T given by A048212.at n=43A048221
- Primes that yield a different prime when rotated by 180 degrees.at n=27A048890
- Primes of the form 30*p + 1 where p is also prime.at n=22A051646
- Numbers n such that phi(reversal(n)) = reversal(phi(n)). Ignore leading 0's.at n=13A069282
- Primes with either no internal digits or all internal digits are 9.at n=45A069684
- Rounded volume of a regular tetrahedron with edge length n.at n=39A071399
- Primes that are still primes when turned upsided down.at n=31A080788
- Balanced primes of order four.at n=6A082079
- a(n) = 7*10^n - 9.at n=2A086945
- Primes p such that the sum of the digits of p is not prime, but the sum of the squares of the digits of p is prime.at n=9A091362
- Primes p such that the sum of the digits of p is not prime, but the sum of each digit raised to the 4th power is prime.at n=4A091368
- First of 9 consecutive primes in a 3 X 3 spiral wherein the mean of all 8 sums is prime.at n=25A094454
- a(n) = 997*n + 1009.at n=6A100776
- Numbers n such that 8*10^n + 5*R_n + 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.at n=17A103086
- Primes with digit sum = 25.at n=31A106763