21512809 has 8 divisors (see below), whose sum is σ = 22621320. Its totient is φ = 20428800.

The previous prime is 21512801. The next prime is 21512833. The reversal of 21512809 is 90821512.

It can be written as a sum of positive squares in 4 ways, for example, as 29584 + 21483225 = 172^2 + 4635^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 21512809 - 2³ = 21512801 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21512801) 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, 4312 + ... + 7849.

It is an arithmetic number, because the mean of its divisors is an integer number (2827665).

Almost surely, 2^21512809 is an apocalyptic number.

21512809 is a gapful number since it is divisible by the number (29) formed by its first and last digit.

It is an amenable number.

21512809 is a deficient number, since it is larger than the sum of its proper divisors (1108511).

21512809 is a wasteful number, since it uses less digits than its factorization.

21512809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12251.

The product of its (nonzero) digits is 1440, while the sum is 28.

The square root of 21512809 is about 4638.1902720781. The cubic root of 21512809 is about 278.1200980325.

The spelling of 21512809 in words is "twenty-one million, five hundred twelve thousand, eight hundred nine".