21539561 has 8 divisors (see below), whose sum is σ = 22924800. Its totient is φ = 20167488.

The previous prime is 21539519. The next prime is 21539591. The reversal of 21539561 is 16593512.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21539561 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21539501) 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, 200 + ... + 6566.

It is an arithmetic number, because the mean of its divisors is an integer number (2865600).

Almost surely, 2^21539561 is an apocalyptic number.

It is an amenable number.

21539561 is a deficient number, since it is larger than the sum of its proper divisors (1385239).

21539561 is a wasteful number, since it uses less digits than its factorization.

21539561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6583.

The product of its digits is 8100, while the sum is 32.

The square root of 21539561 is about 4641.0732594950. The cubic root of 21539561 is about 278.2353346017.

The spelling of 21539561 in words is "twenty-one million, five hundred thirty-nine thousand, five hundred sixty-one".