21213925 has 6 divisors (see below), whose sum is σ = 26305298. Its totient is φ = 16971120.

The previous prime is 21213923. The next prime is 21213931. The reversal of 21213925 is 52931212.

It is a happy number.

It can be written as a sum of positive squares in 3 ways, for example, as 2125764 + 19088161 = 1458^2 + 4369^2 .

It is not a de Polignac number, because 21213925 - 2¹ = 21213923 is a prime.

It is a super-2 number, since 2×21213925² = 900061227811250, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (25), and also a Moran number because the ratio is a prime number: 848557 = 21213925 / (2 + 1 + 2 + 1 + 3 + 9 + 2 + 5).

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21213925.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21213923) by changing a digit.

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

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 424254 + ... + 424303.

Almost surely, 2^21213925 is an apocalyptic number.

21213925 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21213925 is a deficient number, since it is larger than the sum of its proper divisors (5091373).

21213925 is an equidigital number, since it uses as much as digits as its factorization.

21213925 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 848567 (or 848562 counting only the distinct ones).

The product of its digits is 1080, while the sum is 25.

The square root of 21213925 is about 4605.8576834288. The cubic root of 21213925 is about 276.8260843153.

The spelling of 21213925 in words is "twenty-one million, two hundred thirteen thousand, nine hundred twenty-five".