2131
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 7
- Digital Root
- 7
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 1
Divisibility
- Divisor Count
- 2
- Divisor Sum
- 2132
- 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
- 2130
- Möbius Function
- -1
- Radical
- 2131
- 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
- 76
- 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
- 321
- Perfect Power
- no
- Smooth Number
- no
- Carmichael Number
- no
Classification
- Even
- no
- Odd
- yes
Appears in sequences
- a(n) = 4*a(n-1) - a(n-2), with a(0) = 1, a(1) = 1.at n=7A001835
- a(n) = 4*a(n-2) - a(n-4) for n > 1, a(n) = n for n = 0, 1.at n=13A002530
- Primes written in base 4.at n=36A004678
- a(n) = (1 + a(n-1)*a(n-2))/a(n-3), a(0) = a(1) = a(2) = 1.at n=14A005246
- Smallest prime beginning a complete Cunningham chain (of the second kind) of length n.at n=3A005603
- Primes of form 2n^2 - 2n + 19.at n=27A007639
- Coordination sequence T2 for Zeolite Code EMT.at n=38A008087
- Coordination sequence T6 for Zeolite Code MTW.at n=30A008201
- Molien series for A_7.at n=31A008630
- Coordination sequence T3 for Zeolite Code CGF.at n=32A019453
- Numbers k such that the continued fraction for sqrt(k) has period 58.at n=2A020397
- Primes that remain prime through 2 iterations of the function f(x) = 5x + 8.at n=23A023255
- Primes that remain prime through 2 iterations of the function f(x) = 8*x + 5.at n=17A023262
- Primes that remain prime through 2 iterations of function f(x) = 10x + 3.at n=42A023269
- Convolution of A023532 and (1, p(1), p(2), ...).at n=38A023598
- n written in fractional base 5/2.at n=46A024632
- Position of n^2 + 5 in A000408.at n=50A024801
- Index of 9^n within the sequence of the numbers of the form 2^i*9^j.at n=36A025734
- Coordination sequence T3 for Zeolite Code CGS.at n=34A027367
- Triangle read by rows: square of the lower triangular mean matrix.at n=49A027446