2157867721 has 2 divisors, whose sum is σ = 2157867722. Its totient is φ = 2157867720.

The previous prime is 2157867707. The next prime is 2157867737. The reversal of 2157867721 is 1277687512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1351591696 + 806276025 = 36764^2 + 28395^2 .

It is a cyclic number.

It is not a de Polignac number, because 2157867721 - 2⁵ = 2157867689 is a prime.

It is not a weakly prime, because it can be changed into another prime (2157867421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1078933860 + 1078933861.

It is an arithmetic number, because the mean of its divisors is an integer number (1078933861).

Almost surely, 2^2157867721 is an apocalyptic number.

It is an amenable number.

2157867721 is a deficient number, since it is larger than the sum of its proper divisors (1).

2157867721 is an equidigital number, since it uses as much as digits as its factorization.

2157867721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 329280, while the sum is 46.

The square root of 2157867721 is about 46452.8548207750. The cubic root of 2157867721 is about 1292.2353169535.

The spelling of 2157867721 in words is "two billion, one hundred fifty-seven million, eight hundred sixty-seven thousand, seven hundred twenty-one".