21511057 has 4 divisors (see below), whose sum is σ = 21916980. Its totient is φ = 21105136.

The previous prime is 21511031. The next prime is 21511079. The reversal of 21511057 is 75011512.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 19704721 + 1806336 = 4439^2 + 1344^2 .

It is a cyclic number.

It is not a de Polignac number, because 21511057 - 2²³ = 13122449 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21511657) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 202882 + ... + 202987.

It is an arithmetic number, because the mean of its divisors is an integer number (5479245).

Almost surely, 2^21511057 is an apocalyptic number.

It is an amenable number.

21511057 is a deficient number, since it is larger than the sum of its proper divisors (405923).

21511057 is an equidigital number, since it uses as much as digits as its factorization.

21511057 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 405922.

The product of its (nonzero) digits is 350, while the sum is 22.

The square root of 21511057 is about 4638.0014014659. The cubic root of 21511057 is about 278.1125478076.

Adding to 21511057 its reverse (75011512), we get a palindrome (96522569).

The spelling of 21511057 in words is "twenty-one million, five hundred eleven thousand, fifty-seven".