1819
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
- 4
- Divisor Sum
- 1944
- Proper Divisor Sum (Aliquot Sum)
- 125
- 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
- 1696
- Möbius Function
- 1
- Radical
- 1819
- Omega Function (Ω)
- 2
- Little Omega Function (ω)
- 2
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
- 161
- Smith Number
- no
- Vampire Number
- no
Primality
- Prime
- no
- Composite Number
- yes
- Semiprime
- yes
- Squarefree Number
- yes
- Prime Power
- no
- Prime Factorization
- no
- Twin Prime
- no
- Mersenne Prime
- no
- Sophie Germain Prime
- no
- Safe Prime
- no
- Powerful Number
- no
- Achilles Number
- no
- Perfect Power
- no
- Smooth Number
- no
- Carmichael Number
- no
Classification
- Even
- no
- Odd
- yes
Appears in sequences
- a(n) = n concatenated with n + 1.at n=17A001704
- a(1) = 1; for n>1, a(n) = a(n-1) + 1 + sum of distinct prime factors of a(n-1) that are < a(n-1).at n=52A003508
- Convolution of Fibonacci numbers 1,2,3,5,... with themselves.at n=10A004798
- Number of rhyme schemes (see reference for precise definition).at n=6A005002
- In the '3x+1' problem, these values for the starting value set new records for highest point of trajectory before reaching 1.at n=10A006884
- Coordination sequence T1 for Zeolite Code EAB.at n=31A008082
- Coordination sequence T1 for Zeolite Code -CLO.at n=38A009850
- Number of partitions of n into distinct parts, none being 2.at n=49A015744
- Expansion of 1/(1-x^7-x^8-x^9-x^10-x^11-x^12).at n=50A017861
- Numbers k such that the continued fraction for sqrt(k) has period 38.at n=12A020377
- Index of 5^n within sequence of numbers of form 3^i*5^j.at n=49A022338
- a(n) = [ a(n-1)/a(1) + a(n-3)/a(3) + a(n-5)/a(5) + ... ], for n >= 3.at n=24A022865
- '3x+1' record-setters (blowup factor).at n=6A025587
- a(n) = C(4*n,n) - C(4*n,n-4).at n=4A026033
- Pair up the numbers.at n=9A030656
- Positions of record values in A030767.at n=45A030772
- Numbers k such that the continued fraction for sqrt(k) has even period and if the last term of the periodic part is deleted the central term is 41.at n=13A031539
- Numbers k such that the period of the continued fraction for sqrt(k) contains exactly 18 ones.at n=27A031786
- Lucky numbers with size of gaps equal to 8 (lower terms).at n=19A031890
- Lucky numbers with size of gaps equal to 10 (upper terms).at n=19A031893