21634608857 has 4 divisors (see below), whose sum is σ = 21635055156. Its totient is φ = 21634162560.

The previous prime is 21634608847. The next prime is 21634608893. The reversal of 21634608857 is 75880643612.

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 14980780816 + 6653828041 = 122396^2 + 81571^2 .

It is a cyclic number.

It is not a de Polignac number, because 21634608857 - 2¹⁶ = 21634543321 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21634608847) 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, 140144 + ... + 250817.

It is an arithmetic number, because the mean of its divisors is an integer number (5408763789).

Almost surely, 2^21634608857 is an apocalyptic number.

It is an amenable number.

21634608857 is a deficient number, since it is larger than the sum of its proper divisors (446299).

21634608857 is an equidigital number, since it uses as much as digits as its factorization.

21634608857 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 446298.

The product of its (nonzero) digits is 1935360, while the sum is 50.

The spelling of 21634608857 in words is "twenty-one billion, six hundred thirty-four million, six hundred eight thousand, eight hundred fifty-seven".