8515
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
- 2
Divisibility
- Divisor Count
- 8
- Divisor Sum
- 11088
- Proper Divisor Sum (Aliquot Sum)
- 2573
- 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
- 6240
- Möbius Function
- -1
- Radical
- 8515
- 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
- yes
- 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
- 39
- 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) = p*(p-1)/2 for p = prime(n).at n=31A008837
- a(n) = T(2n+1,n+1), T given by A026736.at n=7A026854
- Lucky numbers with size of gaps equal to 20 (lower terms).at n=17A031902
- a(n) = (2*n-1)*(4*n-1).at n=33A033567
- Numbers whose base-5 representation contains exactly two 0's and three 3's.at n=24A045198
- Centered 9-gonal (also known as nonagonal or enneagonal) numbers. Every third triangular number, starting with a(1)=1.at n=43A060544
- Number of heptagonal regions in regular n-gon with all diagonals drawn.at n=58A067154
- Numbers n such that n and its 10's complement are both triangular numbers; that is, n and 10^k - n (where k is the number of digits in n) are triangular numbers.at n=8A068812
- Triangular numbers that are 3-almost primes.at n=37A075875
- Positive integers not expressible as the sum of a prime and a triangular number.at n=53A076768
- Numbers k for which the sums of prime factors (ignoring multiplicity) of sigma(k) and phi(k) are equal but the sets of prime factors of sigma and phi are different.at n=29A081378
- Binomial coefficients C(p, k), 2<=k<=p-2, sorted, with duplicates removed, p being prime.at n=46A082581
- a(n) = smallest k where (10^k+1)=0 mod prime(n)^2, or 0 if no such k exists.at n=31A086981
- Triangle read by rows in which the n-th row contains the n smallest triangular numbers with the least significant digits of the n-th triangular number.at n=12A095225
- Index k in A095773 where a string of n identical values occurs.at n=22A096183
- Triangle read by rows: T(n,k) is the number of Motzkin paths of length n having k returns (i.e., down steps hitting the x-axis).at n=52A097612
- Least triangular number divisible by n-th prime.at n=31A112456
- Diagonal sums of correlation triangle for floor((n+2)/2).at n=50A115264
- Triangular numbers whose digit reversal is a semiprime (A001358).at n=38A115742
- Triangular numbers for which the sum of the digits is a prime number.at n=25A117512