21009513 has 8 divisors (see below), whose sum is σ = 32014528. Its totient is φ = 12005424.

The previous prime is 21009509. The next prime is 21009523. The reversal of 21009513 is 31590012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21009513 - 2² = 21009509 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21), and also a Moran number because the ratio is a prime number: 1000453 = 21009513 / (2 + 1 + 0 + 0 + 9 + 5 + 1 + 3).

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21009513.

It is not an unprimeable number, because it can be changed into a prime (21009503) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 500206 + ... + 500247.

It is an arithmetic number, because the mean of its divisors is an integer number (4001816).

Almost surely, 2^21009513 is an apocalyptic number.

It is an amenable number.

21009513 is a deficient number, since it is larger than the sum of its proper divisors (11005015).

21009513 is a wasteful number, since it uses less digits than its factorization.

21009513 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1000463.

The product of its (nonzero) digits is 270, while the sum is 21.

The square root of 21009513 is about 4583.6135308291. The cubic root of 21009513 is about 275.9340711041.

Adding to 21009513 its reverse (31590012), we get a palindrome (52599525).

The spelling of 21009513 in words is "twenty-one million, nine thousand, five hundred thirteen".