15225
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
- 24
- Divisor Sum
- 29760
- Proper Divisor Sum (Aliquot Sum)
- 14535
- Abundant Number
- no
- Perfect Number
- no
- Deficient Number
- yes
- Weird Number
- no
- Untouchable Number
- no
- Primitive Abundant
- no
Derived Values
- Euler's Totient
- 6720
- Möbius Function
- 0
- Radical
- 3045
- Omega Function (Ω)
- 5
- Little Omega Function (ω)
- 4
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
- yes
- Narcissistic Number
- no
- Collatz Steps
- 84
- Smith Number
- no
- Vampire Number
- no
Primality
- Prime
- no
- Composite Number
- yes
- Semiprime
- no
- Squarefree Number
- no
- 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
- Centered octahedral numbers (crystal ball sequence for cubic lattice).at n=22A001845
- a(n) = 3^n reduced modulo 2^n.at n=14A002380
- a(n) = C(n,1) + C(n,2) + C(n,3), or n*(n^2 + 5)/6.at n=45A004006
- a(1) = 3; a(n+1) = a(n)-th nonprime, where nonprimes begin at 0.at n=39A025000
- a(n) = (2*n-1)*(4*n-1).at n=44A033567
- Numbers k such that phi(k) is equal to A008473(k).at n=12A039779
- a(n) is the decimal concatenation of n and n^2.at n=14A053061
- Partial sums of A054469.at n=9A054470
- Number of 3 X 3 matrices, with elements from {0,...,n}, having the property that the middle element of each of the eight 3-element horizontal, vertical and diagonal lines equals the average of the two end elements.at n=44A059329
- Triangular numbers with sum of digits = 15.at n=26A068130
- Triangular numbers of the form 21*k.at n=33A069499
- Numbers k such that phi(k) = Sum_{d|k} core(d) where core(x) is the squarefree part of x (A007913).at n=10A074786
- Triangular numbers which are 5-almost primes.at n=36A076579
- a(1) = 1, a(n+1)= smallest triangular number greater than the n-th partial sum.at n=13A076971
- Rearrangement of triangular numbers such that the sum of two consecutive terms is a palindrome.at n=43A082980
- Triangular numbers whose sum of aliquot divisors is also a triangular number.at n=11A083675
- Integers k such that nextprime(k^5) - prevprime(k^5) = 4.at n=13A090123
- Take pairs (a, b), sorted on a, such that T(a)+T(b)=concatenation of a and b, where T(k) is the k-th triangular number A000217(k). Sequence gives values of a.at n=26A096031
- a(n) = C(n-2,2)+C(n-5,5)+...+C(n-(3*floor((n-3)/3)+2),3*floor((n-3)/3)+2).at n=23A101551
- a(n) = n*(n+1)*(n^2 + 21*n + 50)/24.at n=19A101854