21645690415 has 4 divisors (see below), whose sum is σ = 25974828504. Its totient is φ = 17316552328.

The previous prime is 21645690401. The next prime is 21645690439. The reversal of 21645690415 is 51409654612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21645690415 - 2¹⁵ = 21645657647 is a prime.

It is a Duffinian number.

It is a congruent 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, 2164569037 + ... + 2164569046.

It is an arithmetic number, because the mean of its divisors is an integer number (6493707126).

Almost surely, 2^21645690415 is an apocalyptic number.

21645690415 is a deficient number, since it is larger than the sum of its proper divisors (4329138089).

21645690415 is an equidigital number, since it uses as much as digits as its factorization.

21645690415 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4329138088.

The product of its (nonzero) digits is 259200, while the sum is 43.

The spelling of 21645690415 in words is "twenty-one billion, six hundred forty-five million, six hundred ninety thousand, four hundred fifteen".