21690409 has 8 divisors (see below), whose sum is σ = 23800392. Its totient is φ = 19643520.

The previous prime is 21690407. The next prime is 21690413. The reversal of 21690409 is 90409612.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 40000 + 21650409 = 200^2 + 4653^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21690409 - 2¹ = 21690407 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21690407) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 15052 + ... + 16429.

It is an arithmetic number, because the mean of its divisors is an integer number (2975049).

Almost surely, 2^21690409 is an apocalyptic number.

It is an amenable number.

21690409 is a deficient number, since it is larger than the sum of its proper divisors (2109983).

21690409 is a wasteful number, since it uses less digits than its factorization.

21690409 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 31547.

The product of its (nonzero) digits is 3888, while the sum is 31.

The square root of 21690409 is about 4657.2963186810. The cubic root of 21690409 is about 278.8833460154.

The spelling of 21690409 in words is "twenty-one million, six hundred ninety thousand, four hundred nine".