21405425 has 24 divisors (see below), whose sum is σ = 27720696. Its totient is φ = 16381440.

The previous prime is 21405409. The next prime is 21405427. The reversal of 21405425 is 52450412.

21405425 = 3271² + 3272².

It is a happy number.

It can be written as a sum of positive squares in 12 ways, for example, as 5779216 + 15626209 = 2404^2 + 3953^2 .

It is not a de Polignac number, because 21405425 - 2⁴ = 21405409 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21405425.

It is not an unprimeable number, because it can be changed into a prime (21405427) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 67367 + ... + 67683.

It is an arithmetic number, because the mean of its divisors is an integer number (1155029).

Almost surely, 2^21405425 is an apocalyptic number.

21405425 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21405425 is the 3272-nd centered square number.

It is an amenable number.

21405425 is a deficient number, since it is larger than the sum of its proper divisors (6315271).

21405425 is a wasteful number, since it uses less digits than its factorization.

21405425 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 437 (or 432 counting only the distinct ones).

The product of its (nonzero) digits is 1600, while the sum is 23.

The square root of 21405425 is about 4626.5997233389. The cubic root of 21405425 is about 277.6565683026.

Adding to 21405425 its reverse (52450412), we get a palindrome (73855837).

The spelling of 21405425 in words is "twenty-one million, four hundred five thousand, four hundred twenty-five".