21705580657 has 2 divisors, whose sum is σ = 21705580658. Its totient is φ = 21705580656.

The previous prime is 21705580609. The next prime is 21705580703. The reversal of 21705580657 is 75608550712.

It is an a-pointer prime, because the next prime (21705580703) can be obtained adding 21705580657 to its sum of digits (46).

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14741845056 + 6963735601 = 121416^2 + 83449^2 .

It is a cyclic number.

It is not a de Polignac number, because 21705580657 - 2¹⁵ = 21705547889 is a prime.

It is a super-2 number, since 2×21705580657² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21705580157) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10852790328 + 10852790329.

It is an arithmetic number, because the mean of its divisors is an integer number (10852790329).

Almost surely, 2^21705580657 is an apocalyptic number.

It is an amenable number.

21705580657 is a deficient number, since it is larger than the sum of its proper divisors (1).

21705580657 is an equidigital number, since it uses as much as digits as its factorization.

21705580657 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 588000, while the sum is 46.

The spelling of 21705580657 in words is "twenty-one billion, seven hundred five million, five hundred eighty thousand, six hundred fifty-seven".