12781
domain: N
Properties
Digital Properties
- Digit Count
- 5
- Digit Sum
- 19
- Digital Root
- 1
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 2
- Divisor Sum
- 12782
- Proper Divisor Sum (Aliquot Sum)
- 1
- Abundant Number
- no
- Perfect Number
- no
- Deficient Number
- yes
- Weird Number
- no
- Untouchable Number
- no
- Primitive Abundant
- no
Derived Values
- Euler's Totient
- 12780
- Möbius Function
- -1
- Radical
- 12781
- 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
- 76
- 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
- 1524
- Perfect Power
- no
- Smooth Number
- no
- Carmichael Number
- no
Classification
- Even
- no
- Odd
- yes
Appears in sequences
- Expansion of x/(1 - 10*x - 9*x^2).at n=5A015591
- Quadruples of different integers from [ 1,n ] with no common factors between triples.at n=27A015625
- Quadruples of different integers from [ 2,n ] with no common factors between triples.at n=27A015629
- a(n) = least m such that if r and s in {1/1, 1/3, 1/5, ..., 1/(2n-1)} satisfy r < s, then r < k/m < (k+4)/m < s for some integer k.at n=37A024847
- Numbers k such that the period of the continued fraction for sqrt(k) contains exactly 52 ones.at n=39A031820
- Sequence of 2 Pythagorean triangles, each with a leg and hypotenuse prime. The leg of the second triangle is the hypotenuse of the first.at n=40A048270
- Smallest prime larger than square of n-th prime.at n=29A062772
- Primes which can be expressed as concatenation of cubes.at n=34A066592
- a(1) = 1, a(n) = smallest prime number not already used such that concatenation of a(k) and a(n) is composite for all k = 1 to n-1.at n=40A075612
- Numbers p such that p = (prime(n)+ prime(n+3))/2 is prime for prime indices n=2, 3, 5...at n=19A098039
- E.g.f. exp( x*(1+x)/(1-x) ).at n=6A112242
- Primes whose digit reversal is a triangular number.at n=9A115705
- a(2*n+1) = 9*a(n), a(2*n+2) = 10*a(n) + a(n-1).at n=30A116555
- Numbers n such that F(2*n - 1) is prime, where F(m) is a Fibonacci number.at n=26A117595
- Primes for which the weight as defined in A117078 is 11 and the gap as defined in A001223 is 10.at n=16A119596
- Primes p such that p^2-p-1 and p^2-p+1 are twin primes.at n=31A120364
- Mountain primes.at n=30A134951
- Prime numbers n such that n^2 +- (n-1) are primes.at n=33A137459
- Prime numbers p such that p +- ((p-1)/3) are primes.at n=11A137703
- Primes of the form k^2 + 12.at n=18A138368