21390625 has 21 divisors (see below), whose sum is σ = 27480117. Its totient is φ = 16650000.

The previous prime is 21390619. The next prime is 21390631. The reversal of 21390625 is 52609312.

The square root of 21390625 is 4625.

It is a perfect power (a square), and thus also a powerful number.

It is an interprime number because it is at equal distance from previous prime (21390619) and next prime (21390631).

It can be written as a sum of positive squares in 10 ways, for example, as 21372129 + 18496 = 4623^2 + 136^2 .

It is not a de Polignac number, because 21390625 - 2³ = 21390617 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21390593 and 21390602.

It is an unprimeable number.

It is a polite number, since it can be written in 20 ways as a sum of consecutive naturals, for example, 578107 + ... + 578143.

It is an arithmetic number, because the mean of its divisors is an integer number (1308577).

Almost surely, 2^21390625 is an apocalyptic number.

21390625 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21390625 is the 4625-th square number.

21390625 is the 2313-rd centered octagonal number.

It is an amenable number.

21390625 is a deficient number, since it is larger than the sum of its proper divisors (6089492).

21390625 is an frugal number, since it uses more digits than its factorization.

21390625 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 104 (or 42 counting only the distinct ones).

The product of its (nonzero) digits is 3240, while the sum is 28.

The cubic root of 21390625 is about 277.5925617147.

Adding to 21390625 its reverse (52609312), we get a palindrome (73999937).

The spelling of 21390625 in words is "twenty-one million, three hundred ninety thousand, six hundred twenty-five".