21965409 has 12 divisors (see below), whose sum is σ = 31769556. Its totient is φ = 14624352.

The previous prime is 21965371. The next prime is 21965413. The reversal of 21965409 is 90456912.

21965409 is a `hidden beast` number, since 21 + 96 + 540 + 9 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 10595025 + 11370384 = 3255^2 + 3372^2 .

It is not a de Polignac number, because 21965409 - 2²⁴ = 5188193 is a prime.

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (21965459) 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, 10147 + ... + 12119.

It is an arithmetic number, because the mean of its divisors is an integer number (2647463).

Almost surely, 2^21965409 is an apocalyptic number.

It is an amenable number.

21965409 is a deficient number, since it is larger than the sum of its proper divisors (9804147).

21965409 is a wasteful number, since it uses less digits than its factorization.

21965409 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3216 (or 3213 counting only the distinct ones).

The product of its (nonzero) digits is 19440, while the sum is 36.

The square root of 21965409 is about 4686.7268962465. The cubic root of 21965409 is about 280.0569994503.

The spelling of 21965409 in words is "twenty-one million, nine hundred sixty-five thousand, four hundred nine".