21043775657 has 2 divisors, whose sum is σ = 21043775658. Its totient is φ = 21043775656.

The previous prime is 21043775609. The next prime is 21043775659. The reversal of 21043775657 is 75657734012.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15890115136 + 5153660521 = 126056^2 + 71789^2 .

It is a cyclic number.

It is not a de Polignac number, because 21043775657 - 2²⁰ = 21042727081 is a prime.

Together with 21043775659, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21043775659) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10521887828 + 10521887829.

It is an arithmetic number, because the mean of its divisors is an integer number (10521887829).

Almost surely, 2^21043775657 is an apocalyptic number.

It is an amenable number.

21043775657 is a deficient number, since it is larger than the sum of its proper divisors (1).

21043775657 is an equidigital number, since it uses as much as digits as its factorization.

21043775657 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1234800, while the sum is 47.

The spelling of 21043775657 in words is "twenty-one billion, forty-three million, seven hundred seventy-five thousand, six hundred fifty-seven".