21156957257 has 2 divisors, whose sum is σ = 21156957258. Its totient is φ = 21156957256.

The previous prime is 21156957251. The next prime is 21156957293. The reversal of 21156957257 is 75275965112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11661624121 + 9495333136 = 107989^2 + 97444^2 .

It is a cyclic number.

It is not a de Polignac number, because 21156957257 - 2⁶ = 21156957193 is a prime.

It is not a weakly prime, because it can be changed into another prime (21156957251) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10578478628 + 10578478629.

It is an arithmetic number, because the mean of its divisors is an integer number (10578478629).

Almost surely, 2^21156957257 is an apocalyptic number.

It is an amenable number.

21156957257 is a deficient number, since it is larger than the sum of its proper divisors (1).

21156957257 is an equidigital number, since it uses as much as digits as its factorization.

21156957257 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1323000, while the sum is 50.

The spelling of 21156957257 in words is "twenty-one billion, one hundred fifty-six million, nine hundred fifty-seven thousand, two hundred fifty-seven".