21396904493 has 4 divisors (see below), whose sum is σ = 21397207260. Its totient is φ = 21396601728.

The previous prime is 21396904469. The next prime is 21396904523. The reversal of 21396904493 is 39440969312.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 9094101769 + 12302802724 = 95363^2 + 110918^2 .

It is a cyclic number.

It is not a de Polignac number, because 21396904493 - 2¹⁰ = 21396903469 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21396904693) 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, 17213 + ... + 207581.

It is an arithmetic number, because the mean of its divisors is an integer number (5349301815).

Almost surely, 2^21396904493 is an apocalyptic number.

It is an amenable number.

21396904493 is a deficient number, since it is larger than the sum of its proper divisors (302767).

21396904493 is a wasteful number, since it uses less digits than its factorization.

21396904493 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 302766.

The product of its (nonzero) digits is 1259712, while the sum is 50.

The spelling of 21396904493 in words is "twenty-one billion, three hundred ninety-six million, nine hundred four thousand, four hundred ninety-three".