15931
domain: N
Properties
Digital Properties
- Digit Count
- 5
- 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
- 16200
- Proper Divisor Sum (Aliquot Sum)
- 269
- Abundant Number
- no
- Perfect Number
- no
- Deficient Number
- yes
- Weird Number
- no
- Untouchable Number
- no
- Primitive Abundant
- no
Derived Values
- Euler's Totient
- 15664
- Möbius Function
- 1
- Radical
- 15931
- 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
- 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
- 53
- 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
- Numbers k such that 39*2^k + 1 is prime.at n=41A002269
- a(n) = p*(p-1)/2 for p = prime(n).at n=40A008837
- Lexicographically earliest sequence of pairwise coprime triangular numbers.at n=11A034792
- a(n) = 49*(n*(n+1)/2) + 6.at n=25A061792
- Composite numbers whose divisors (except 1) all contain the digit 9.at n=25A062680
- Triangular numbers which are the product of two primes.at n=16A068443
- Triangular numbers with property that swapping first and last digits also gives a triangular number.at n=37A069708
- a(n) = (25*n^2 - 15*n + 2)/2.at n=36A080857
- Sort the digits of these triangular numbers into descending order and drop zeros to get primes.at n=24A082923
- Triangular numbers whose sum of aliquot divisors is a prime number.at n=15A083676
- a(n) = smallest k where (10^k+1)=0 mod prime(n)^2, or 0 if no such k exists.at n=40A086981
- Least triangular number divisible by n-th prime.at n=40A112456
- Triangular numbers for which the sum of the digits is a prime number.at n=37A117512
- Triangular numbers with only odd digits.at n=17A117960
- Triangular numbers with at most two distinct prime factors.at n=34A119663
- Semiprimes in A006987(n), or semiprime binomial coefficients: C(n,k), 2 <= k <= n-2.at n=17A124000
- Triangular numbers congruent to 1 or 5 mod 6.at n=29A128880
- Product p*q of two primes with q = 2*p + 1.at n=9A156592
- Triangular numbers which are sums of 5 consecutive primes.at n=6A173421
- Numbers k such that 2^k-61 is prime.at n=36A182156