557720021 has 4 divisors (see below), whose sum is σ = 559008492. Its totient is φ = 556431552.

The previous prime is 557720017. The next prime is 557720057. The reversal of 557720021 is 120027755.

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 16924996 + 540795025 = 4114^2 + 23255^2 .

It is a cyclic number.

It is not a de Polignac number, because 557720021 - 2² = 557720017 is a prime.

It is a super-2 number, since 2×557720021² = 622103243648480882, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (557720321) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 643586 + ... + 644451.

It is an arithmetic number, because the mean of its divisors is an integer number (139752123).

Almost surely, 2^557720021 is an apocalyptic number.

It is an amenable number.

557720021 is a deficient number, since it is larger than the sum of its proper divisors (1288471).

557720021 is a wasteful number, since it uses less digits than its factorization.

557720021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1288470.

The product of its (nonzero) digits is 4900, while the sum is 29.

The square root of 557720021 is about 23616.0966503781. The cubic root of 557720021 is about 823.1369141214.

Adding to 557720021 its reverse (120027755), we get a palindrome (677747776).

The spelling of 557720021 in words is "five hundred fifty-seven million, seven hundred twenty thousand, twenty-one".