21292409 has 4 divisors (see below), whose sum is σ = 22026660. Its totient is φ = 20558160.

The previous prime is 21292393. The next prime is 21292417. The reversal of 21292409 is 90429212.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 9320809 + 11971600 = 3053^2 + 3460^2 .

It is a cyclic number.

It is not a de Polignac number, because 21292409 - 2⁴ = 21292393 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (29), and also a Moran number because the ratio is a prime number: 734221 = 21292409 / (2 + 1 + 2 + 9 + 2 + 4 + 0 + 9).

It is not an unprimeable number, because it can be changed into a prime (21292429) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 367082 + ... + 367139.

It is an arithmetic number, because the mean of its divisors is an integer number (5506665).

Almost surely, 2^21292409 is an apocalyptic number.

21292409 is a gapful number since it is divisible by the number (29) formed by its first and last digit.

It is an amenable number.

21292409 is a deficient number, since it is larger than the sum of its proper divisors (734251).

21292409 is an equidigital number, since it uses as much as digits as its factorization.

21292409 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 734250.

The product of its (nonzero) digits is 2592, while the sum is 29.

The square root of 21292409 is about 4614.3698378002. The cubic root of 21292409 is about 277.1670502922.

The spelling of 21292409 in words is "twenty-one million, two hundred ninety-two thousand, four hundred nine".