21021605705 has 4 divisors (see below), whose sum is σ = 25225926852. Its totient is φ = 16817284560.

The previous prime is 21021605687. The next prime is 21021605767. The reversal of 21021605705 is 50750612012.

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 8898714889 + 12122890816 = 94333^2 + 110104^2 .

It is not a de Polignac number, because 21021605705 - 2¹² = 21021601609 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2102160566 + ... + 2102160575.

It is an arithmetic number, because the mean of its divisors is an integer number (6306481713).

Almost surely, 2^21021605705 is an apocalyptic number.

It is an amenable number.

21021605705 is a deficient number, since it is larger than the sum of its proper divisors (4204321147).

21021605705 is an equidigital number, since it uses as much as digits as its factorization.

21021605705 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4204321146.

The product of its (nonzero) digits is 4200, while the sum is 29.

The spelling of 21021605705 in words is "twenty-one billion, twenty-one million, six hundred five thousand, seven hundred five".