6661
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 19
- Digital Root
- 1
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 3
Divisibility
- Divisor Count
- 2
- Divisor Sum
- 6662
- 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
- 6660
- Möbius Function
- -1
- Radical
- 6661
- 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
- yes
- Harshad Number
- no
- Narcissistic Number
- no
- Collatz Steps
- 181
- 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
- yes
- Mersenne Prime
- no
- Sophie Germain Prime
- no
- Safe Prime
- no
- Powerful Number
- no
- Achilles Number
- no
- Prime Index
- 859
- Perfect Power
- no
- Smooth Number
- no
- Carmichael Number
- no
Classification
- Even
- no
- Odd
- yes
Appears in sequences
- Numbers k such that (1,k) is "good".at n=40A000696
- Primes that contain digits 1 and 6 only.at n=3A020454
- Let q_k = p*(p+2) be product of k-th pair of twin primes; sequence gives values of p+2 such that (q_k)^2 > q_{k-i}*q_{k+i} for all 1 <= i <= k-1.at n=41A021007
- Primes that remain prime through 3 iterations of function f(x) = 3x + 8.at n=8A023279
- Primes that remain prime through 3 iterations of function f(x) = 9x + 8.at n=21A023298
- Primes that remain prime through 4 iterations of function f(x) = 6x + 5.at n=15A023317
- Numbers k such that the period of the continued fraction for sqrt(k) contains exactly 68 ones.at n=2A031836
- Primes p such that (p+1)/2 and (p+2)/3 are also primes.at n=19A036570
- Smallest n-digit prime containing only digits 1 and 6, or 0 if no such prime exists.at n=3A036933
- Primes of the form 666*n + 1.at n=3A037029
- Smallest prime containing exactly n 6's.at n=3A037065
- Positive numbers having the same set of digits in base 4 and base 9.at n=28A037427
- Primes with indices that are primes with prime indices.at n=34A038580
- a(n) = A033001(n)/4.at n=33A043307
- Numbers having three 6's in base 10.at n=19A043515
- Numbers whose base-9 representation has exactly 5 runs.at n=9A043634
- Primes that yield a different prime when rotated by 180 degrees.at n=23A048890
- Primes prime(k) for which A049076(k) = 3.at n=23A049079
- a(n) = Sum_{i=0..2n} (-1)^i * T(i,2n-i), array T as in A049735.at n=23A049737
- Numbers n such that 49*2^n-1 is prime.at n=20A050550