21561057 has 12 divisors (see below), whose sum is σ = 35592960. Its totient is φ = 12320568.

The previous prime is 21561041. The next prime is 21561077. The reversal of 21561057 is 75016512.

It is not a de Polignac number, because 21561057 - 2⁴ = 21561041 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21561057.

It is not an unprimeable number, because it can be changed into a prime (21561077) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 171057 + ... + 171182.

It is an arithmetic number, because the mean of its divisors is an integer number (2966080).

Almost surely, 2^21561057 is an apocalyptic number.

It is an amenable number.

21561057 is a deficient number, since it is larger than the sum of its proper divisors (14031903).

21561057 is a wasteful number, since it uses less digits than its factorization.

21561057 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 342252 (or 342249 counting only the distinct ones).

The product of its (nonzero) digits is 2100, while the sum is 27.

The square root of 21561057 is about 4643.3885256351. The cubic root of 21561057 is about 278.3278613750.

Adding to 21561057 its reverse (75016512), we get a palindrome (96577569).

The spelling of 21561057 in words is "twenty-one million, five hundred sixty-one thousand, fifty-seven".