9781
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
- 2
Divisibility
- Divisor Count
- 2
- Divisor Sum
- 9782
- 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
- 9780
- Möbius Function
- -1
- Radical
- 9781
- 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
- 42
- 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
- 1206
- Perfect Power
- no
- Smooth Number
- no
- Carmichael Number
- no
Classification
- Even
- no
- Odd
- yes
Appears in sequences
- Numbers k such that the period of the continued fraction for sqrt(k) contains exactly 74 ones.at n=5A031842
- Numbers k such that 47^k - 46^k is prime.at n=5A062613
- Numbers p from A001125 such that 2*p-3 is prime.at n=16A063939
- a(1) = 4; a(n) is smallest number > a(n-1) such that the juxtaposition a(1)a(2)...a(n) is a prime.at n=45A074341
- a(1) = 1; for n>1, a(n) = smallest prime > a(n-1) such that a(1)*...*a(n) + 2 is a prime.at n=46A085013
- Primes p such that (p-11)/10 is also a prime.at n=42A089442
- Beginning with 1, numbers such that the differences a(k)-a(k-1) are distinct and every concatenation n>1 is prime.at n=46A090504
- a(n) = Sum_{i+j+k=n, 0<=j<=i<=k<=n} (n+k)!/(i! * j! * (2*k)!).at n=8A092466
- Value of C in y = x^2 + 9x + C such that y is prime for all x = 0 to 5.at n=11A097437
- Primes of the form 47n+5.at n=28A100760
- Start with 34 and repeatedly reverse the digits and add 16 to get the next term.at n=18A119454
- a(n) = 3 + floor((2 + Sum_{j=1..n-1} a(j))/4).at n=36A120162
- a(0) = 9; for n>0, a(n) is determined by the rule that the concatenation of the leading terms of the difference triangle is the same as the concatenation of the digits of the sequence.at n=12A125004
- Numbers k such that Lucas(4k)/7 is prime.at n=11A129745
- Prime numbers n such that n^2 +- (n-1) are primes.at n=32A137459
- Primes of the form x^2+101y^2.at n=37A139489
- Primes of the form 24x^2+24xy+61y^2.at n=38A140009
- Primes of the form 21x^2+88y^2.at n=37A140036
- Primes of the form 21x^2+12xy+76y^2.at n=39A140622
- Primes congruent to 16 mod 31.at n=41A142020