15621
domain: N
Properties
Digital Properties
- Digit Count
- 5
- Digit Sum
- 15
- Digital Root
- 6
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 2
Divisibility
- Divisor Count
- 8
- Divisor Sum
- 21504
- Proper Divisor Sum (Aliquot Sum)
- 5883
- Abundant Number
- no
- Perfect Number
- no
- Deficient Number
- yes
- Weird Number
- no
- Untouchable Number
- no
- Primitive Abundant
- no
Derived Values
- Euler's Totient
- 10080
- Möbius Function
- -1
- Radical
- 15621
- Omega Function (Ω)
- 3
- Little Omega Function (ω)
- 3
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
- 102
- Smith Number
- no
- Vampire Number
- no
Primality
- Prime
- no
- Composite Number
- yes
- Semiprime
- no
- 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^(n+1) - n + 1.at n=5A014293
- n^3*a(n) is the number of circles in complex projective plane tangent to three smooth curves of degree n in general position.at n=23A030653
- "Orderly" Friedman numbers (or "good" or "nice" Friedman numbers): Friedman numbers (A036057) where the construction digits are used in the proper order.at n=25A080035
- a(n) = (4*n+3)*(4*n+7).at n=30A085027
- G.f. A(x) satisfies: A(x)^4 equals the g.f. of A110638, which consists entirely of numbers 1 through 8.at n=11A112572
- a(n) = Fibonacci(n) mod n^3.at n=31A132636
- First trisection of A061037 (Balmer line series of the hydrogen atom).at n=41A142590
- a(n) = (8*n+3)*(8*n+7).at n=15A146301
- a(n) = 100*n^2 + 100*n + 21.at n=12A152161
- a(n) = 5^n - 4.at n=5A164785
- Monotonic ordering of nonnegative differences 5^i-4^j, for 40>= i>=0, j>=0.at n=27A192162
- Square array T(n,k) = k^n - k + 1 read by antidiagonals.at n=49A193871
- Friedman numbers n such that n+1 is also a Friedman number.at n=35A195420
- a(n) = 8*n^2 + 3*n + 1.at n=44A236267
- a(n) = prime(n)^2 - 4*prime(n).at n=28A245034
- Composite x such that [(x-1)' + (x+1)'] / x' is an integer, where x' is the arithmetic derivative of x.at n=4A246769
- Positive solutions of Monkey and Coconuts Problem for the classic case (5 sailors, 1 coconut to the monkey): a(n) = 15625*n - 4 for n >= 1.at n=0A254029
- Number of length 3 1..(n+1) arrays with every leading partial sum divisible by 2, 3, 5 or 7.at n=31A258634
- a(n) = 2*a(n-1) - a(n-2) + a(n-4) for n>3, a(0)=2, a(1)=3, a(2)=5, a(3)=7, a sequence related to Lucas numbers.at n=19A291660
- Starts of runs of at least 3 consecutive odd numbers whose prime factors are all prime-indexed primes.at n=19A357168