21643304657 has 4 divisors (see below), whose sum is σ = 23308174260. Its totient is φ = 19978435056.

The previous prime is 21643304651. The next prime is 21643304677. The reversal of 21643304657 is 75640334612.

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 9371982481 + 12271322176 = 96809^2 + 110776^2 .

It is a cyclic number.

It is not a de Polignac number, because 21643304657 - 2²⁶ = 21576195793 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21643304651) 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, 832434782 + ... + 832434807.

It is an arithmetic number, because the mean of its divisors is an integer number (5827043565).

Almost surely, 2^21643304657 is an apocalyptic number.

It is an amenable number.

21643304657 is a deficient number, since it is larger than the sum of its proper divisors (1664869603).

21643304657 is a wasteful number, since it uses less digits than its factorization.

21643304657 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1664869602.

The product of its (nonzero) digits is 362880, while the sum is 41.

The spelling of 21643304657 in words is "twenty-one billion, six hundred forty-three million, three hundred four thousand, six hundred fifty-seven".