1721
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 11
- Digital Root
- 2
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 2
- Divisor Sum
- 1722
- 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
- 1720
- Möbius Function
- -1
- Radical
- 1721
- 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
- 55
- 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
- 268
- Perfect Power
- no
- Smooth Number
- no
- Carmichael Number
- no
Classification
- Even
- no
- Odd
- yes
Appears in sequences
- Primes of the form k^2 - k - 1.at n=23A002327
- a(n) = floor(n*phi^10), where phi is the golden ratio, A001622.at n=14A004925
- Number of certain self-avoiding walks with n steps on square lattice (see reference for precise definition).at n=15A006142
- a(n) = n OR n^2 (applied to binary expansions).at n=40A007745
- Primes p == 1 (mod 8), p = a^2 +64*b^2 such that y^2 = x^3 + p*x has rank 0.at n=6A007765
- For any circular arrangement of 0..n-1, let S = sum of squares of every sum of two contiguous numbers; then a(n) = # of distinct values of S.at n=21A007773
- Expansion of (1+x^9)/((1-x)*(1-x^2)*(1-x^3)*(1-x^4)).at n=49A008770
- A B_2 sequence: a(n) = least value such that the sequence increases and pairwise sums of distinct terms are all distinct.at n=34A010672
- Partial sums of primes, if 1 is regarded as a prime (as it was until quite recently, see A008578).at n=31A014284
- Primes p == 1 mod 8 such that 2 and -2 are both 4th powers (one implies other) mod p.at n=28A014754
- Numbers k such that the continued fraction for sqrt(k) has period 27.at n=6A020366
- n-th prime p(k) such that p(k) + p(k+6) = p(k+2) + p(k+4).at n=30A022891
- Primes that remain prime through 2 iterations of the function f(x) = 5x + 4.at n=19A023253
- Primes that remain prime through 3 iterations of function f(x) = 5x + 4.at n=5A023284
- Primes that remain prime through 3 iterations of function f(x) = 6x + 5.at n=22A023288
- Primes that remain prime through 4 iterations of function f(x) = 6x + 5.at n=6A023317
- Coordination sequence T4 for Zeolite Code IFR.at n=29A024985
- a(n) = n + (n+1)^2.at n=40A028387
- Previous prime concatenated with this prime p is a prime.at n=39A030460
- a(n) = prime(6*n - 2).at n=44A031380