21388225 has 12 divisors (see below), whose sum is σ = 27436860. Its totient is φ = 16520000.

The previous prime is 21388219. The next prime is 21388249. The reversal of 21388225 is 52288312.

It can be written as a sum of positive squares in 6 ways, for example, as 703921 + 20684304 = 839^2 + 4548^2 .

It is not a de Polignac number, because 21388225 - 2¹⁵ = 21355457 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 14026 + ... + 15475.

It is an arithmetic number, because the mean of its divisors is an integer number (2286405).

Almost surely, 2^21388225 is an apocalyptic number.

21388225 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21388225 is a deficient number, since it is larger than the sum of its proper divisors (6048635).

21388225 is a wasteful number, since it uses less digits than its factorization.

21388225 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29540 (or 29535 counting only the distinct ones).

The product of its digits is 7680, while the sum is 31.

The square root of 21388225 is about 4624.7405332624. The cubic root of 21388225 is about 277.5821794862.

The spelling of 21388225 in words is "twenty-one million, three hundred eighty-eight thousand, two hundred twenty-five".