21557747 has 2 divisors, whose sum is σ = 21557748. Its totient is φ = 21557746.

The previous prime is 21557737. The next prime is 21557773. The reversal of 21557747 is 74775512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21557747 - 2²⁰ = 20509171 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21557747.

It is not a weakly prime, because it can be changed into another prime (21557707) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10778873 + 10778874.

It is an arithmetic number, because the mean of its divisors is an integer number (10778874).

Almost surely, 2^21557747 is an apocalyptic number.

21557747 is a deficient number, since it is larger than the sum of its proper divisors (1).

21557747 is an equidigital number, since it uses as much as digits as its factorization.

21557747 is an evil number, because the sum of its binary digits is even.

The product of its digits is 68600, while the sum is 38.

The square root of 21557747 is about 4643.0320912094. The cubic root of 21557747 is about 278.3136179118.

The spelling of 21557747 in words is "twenty-one million, five hundred fifty-seven thousand, seven hundred forty-seven".