21391798 has 16 divisors (see below), whose sum is σ = 33473664. Its totient is φ = 10241280.

The previous prime is 21391793. The next prime is 21391801. The reversal of 21391798 is 89719312.

It is a self number, because there is not a number n which added to its sum of digits gives 21391798.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21391793) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is an upside-down number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4236 + ... + 7792.

It is an arithmetic number, because the mean of its divisors is an integer number (2092104).

Almost surely, 2^21391798 is an apocalyptic number.

21391798 is a deficient number, since it is larger than the sum of its proper divisors (12081866).

21391798 is a wasteful number, since it uses less digits than its factorization.

21391798 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3687.

The product of its digits is 27216, while the sum is 40.

The square root of 21391798 is about 4625.1268090724. The cubic root of 21391798 is about 277.5976357463.

The spelling of 21391798 in words is "twenty-one million, three hundred ninety-one thousand, seven hundred ninety-eight".