21865409 has 12 divisors (see below), whose sum is σ = 23714964. Its totient is φ = 20142432.

The previous prime is 21865399. The next prime is 21865411. The reversal of 21865409 is 90456812.

It can be written as a sum of positive squares in 2 ways, for example, as 9241600 + 12623809 = 3040^2 + 3553^2 .

It is not a de Polignac number, because 21865409 - 2¹² = 21861313 is a prime.

It is a super-2 number, since 2×21865409² = 956192221474562, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21865439) 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, 12539 + ... + 14175.

It is an arithmetic number, because the mean of its divisors is an integer number (1976247).

Almost surely, 2^21865409 is an apocalyptic number.

It is an amenable number.

21865409 is a deficient number, since it is larger than the sum of its proper divisors (1849555).

21865409 is a wasteful number, since it uses less digits than its factorization.

21865409 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1712 (or 1693 counting only the distinct ones).

The product of its (nonzero) digits is 17280, while the sum is 35.

The square root of 21865409 is about 4676.0463000274. The cubic root of 21865409 is about 279.6313558476.

The spelling of 21865409 in words is "twenty-one million, eight hundred sixty-five thousand, four hundred nine".