21398945 has 4 divisors (see below), whose sum is σ = 25678740. Its totient is φ = 17119152.

The previous prime is 21398941. The next prime is 21398957. The reversal of 21398945 is 54989312.

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 5326864 + 16072081 = 2308^2 + 4009^2 .

It is a cyclic number.

It is not a de Polignac number, because 21398945 - 2² = 21398941 is a prime.

It is a super-2 number, since 2×21398945² = 915829694226050, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21398941) 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, 2139890 + ... + 2139899.

It is an arithmetic number, because the mean of its divisors is an integer number (6419685).

Almost surely, 2^21398945 is an apocalyptic number.

It is an amenable number.

21398945 is a deficient number, since it is larger than the sum of its proper divisors (4279795).

21398945 is an equidigital number, since it uses as much as digits as its factorization.

21398945 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4279794.

The product of its digits is 77760, while the sum is 41.

The square root of 21398945 is about 4625.8993720141. The cubic root of 21398945 is about 277.6285474286.

The spelling of 21398945 in words is "twenty-one million, three hundred ninety-eight thousand, nine hundred forty-five".