21812309 has 16 divisors (see below), whose sum is σ = 24121152. Its totient is φ = 19638528.

The previous prime is 21812279. The next prime is 21812353. The reversal of 21812309 is 90321812.

It is a cyclic number.

It is not a de Polignac number, because 21812309 - 2⁸ = 21812053 is a prime.

It is a super-3 number, since 3×21812309³ (a number of 23 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21812389) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 38462 + ... + 39024.

It is an arithmetic number, because the mean of its divisors is an integer number (1507572).

Almost surely, 2^21812309 is an apocalyptic number.

It is an amenable number.

21812309 is a deficient number, since it is larger than the sum of its proper divisors (2308843).

21812309 is a wasteful number, since it uses less digits than its factorization.

21812309 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 676.

The product of its (nonzero) digits is 864, while the sum is 26.

The square root of 21812309 is about 4670.3649750314. The cubic root of 21812309 is about 279.4048114000.

The spelling of 21812309 in words is "twenty-one million, eight hundred twelve thousand, three hundred nine".