1621
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 10
- Digital Root
- 1
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 2
- Divisor Sum
- 1622
- 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
- 1620
- Möbius Function
- -1
- Radical
- 1621
- 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
- 29
- 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
- 257
- 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=19A000696
- Primes of the form 2^q*3^r*5^s + 1.at n=39A002200
- Quintan primes: p = (x^5 + y^5)/(x + y).at n=7A002650
- Divisible only by primes congruent to 4 mod 7.at n=48A004622
- Class 4+ primes (for definition see A005105).at n=26A005108
- Primes p such that (p+1)/2 is prime.at n=29A005383
- From relations between Siegel theta series.at n=13A006476
- From a partition of the integers.at n=26A006628
- Primes with both 10 and -10 as primitive root.at n=47A007349
- Prime(n)*...*prime(a(n)) is the least product of consecutive primes that is non-deficient.at n=27A007684
- Prime(n)*...*prime(a(n)) is the least product of consecutive primes which is abundant.at n=27A007707
- Coordination sequence T3 for Zeolite Code LTN.at n=28A008142
- Expansion of (1+x^9)/((1-x)*(1-x^2)*(1-x^3)*(1-x^4)).at n=48A008770
- Values of k at which the period of the continued fraction for sqrt(k) sets a new record.at n=27A013645
- Primes p==1 (mod 6) such that 3 and -3 are both cubes (one implies other) modulo p.at n=39A014753
- Numbers k such that the continued fraction for sqrt(k) has period 79.at n=0A020418
- Smallest nonempty set S containing prime divisors of 6k+7 for each k in S.at n=42A020604
- n-th prime p(k) such that p(k) + p(k+4) = p(k+1) + p(k+3).at n=47A022887
- Primes p such that 4*p + 7 is also prime.at n=47A023215
- Primes p such that 7*p + 4 is also prime.at n=47A023224