21021640705 has 16 divisors (see below), whose sum is σ = 27626880960. Its totient is φ = 15260557248.

The previous prime is 21021640691. The next prime is 21021640709. The reversal of 21021640705 is 50704612012.

It is a cyclic number.

It is not a de Polignac number, because 21021640705 - 2⁹ = 21021640193 is a prime.

It is a super-2 number, since 2×21021640705² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21021640709) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2736927 + ... + 2744596.

It is an arithmetic number, because the mean of its divisors is an integer number (1726680060).

Almost surely, 2^21021640705 is an apocalyptic number.

It is an amenable number.

21021640705 is a deficient number, since it is larger than the sum of its proper divisors (6605240255).

21021640705 is a wasteful number, since it uses less digits than its factorization.

21021640705 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5481600.

The product of its (nonzero) digits is 3360, while the sum is 28.

The spelling of 21021640705 in words is "twenty-one billion, twenty-one million, six hundred forty thousand, seven hundred five".