641
domain: N
Properties
Digital Properties
- Digit Count
- 3
- 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
- 642
- 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
- 640
- Möbius Function
- -1
- Radical
- 641
- 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
- 51
- Smith 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
- yes
- Safe Prime
- no
- Powerful Number
- no
- Achilles Number
- no
- Prime Index
- 116
- Perfect Power
- no
- Smooth Number
- no
- Carmichael Number
- no
Classification
- Even
- no
- Odd
- yes
Names
- German
- sechshunderteinundvierzig· ordinal: sechshunderteinundvierzigste
- English
- six hundred forty-one· ordinal: six hundred forty-first
- Spanish
- seiscientos cuarenta y uno· ordinal: 641º
- French
- six cent quarante et un· ordinal: six cent quarante et unième
- Italian
- seicentoquarantuno· ordinal: 641º
- Latin
- sescenti quadraginta unus· ordinal: 641.
- Portuguese
- seiscentos e quarenta e um· ordinal: 641º
Appears in sequences
- a(n) is the number of conjugacy classes in the alternating group A_n.at n=22A000702
- Number of twin prime pairs < square of n-th prime.at n=46A000885
- Twin primes.at n=55A001097
- Primes with 3 as smallest primitive root.at n=28A001123
- Irregular table read by rows: row n lists prime factors of 10^n + 1, with multiplicity.at n=48A001271
- Lesser of twin primes.at n=28A001359
- Numbers n such that (10^n + 1)/11 is a prime.at n=7A001562
- Numbers k such that phi(k+2) = phi(k) + 2.at n=44A001838
- G.f.: -1 + Product_{k>=1} (1 + prime(k)*x^prime(k)).at n=24A002099
- Primes of the form 2^q*3^r*5^s + 1.at n=30A002200
- Smallest prime factor of 2^n + 1.at n=31A002586
- Numbers k such that (k^2 + k + 1)/7 is prime.at n=53A002641
- Quartan primes: primes of the form x^4 + y^4, x > 0, y > 0.at n=5A002645
- a(1) = 1; a(2) = 2; a(n) == a(k) (mod n-k) for all 1 < k < n.at n=10A002987
- Primes p with a Fibonacci primitive root g, i.e., such that g^2 = g + 1 (mod p).at n=36A003147
- Numbers that are the sum of 2 positive 4th powers.at n=11A003336
- Numbers that are the sum of 6 positive 4th powers.at n=48A003340
- Numbers that are the sum of 11 positive 6th powers.at n=10A003367
- Numbers that are the sum of 6 positive 7th powers.at n=5A003373
- Discriminants of real quadratic fields with narrow class number 1.at n=51A003655