21625409 has 12 divisors (see below), whose sum is σ = 23995692. Its totient is φ = 19468800.

The previous prime is 21625397. The next prime is 21625453. The reversal of 21625409 is 90452612.

It is a happy number.

It can be written as a sum of positive squares in 6 ways, for example, as 16321600 + 5303809 = 4040^2 + 2303^2 .

It is a de Polignac number, because none of the positive numbers 2^k-21625409 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21625459) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 5369 + ... + 8489.

It is an arithmetic number, because the mean of its divisors is an integer number (1999641).

Almost surely, 2^21625409 is an apocalyptic number.

It is an amenable number.

21625409 is a deficient number, since it is larger than the sum of its proper divisors (2370283).

21625409 is a wasteful number, since it uses less digits than its factorization.

21625409 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3188 (or 3175 counting only the distinct ones).

The product of its (nonzero) digits is 4320, while the sum is 29.

The square root of 21625409 is about 4650.3127851791. The cubic root of 21625409 is about 278.6044891979.

The spelling of 21625409 in words is "twenty-one million, six hundred twenty-five thousand, four hundred nine".