21321729 has 24 divisors (see below), whose sum is σ = 36184512. Its totient is φ = 11927520.

The previous prime is 21321709. The next prime is 21321733. The reversal of 21321729 is 92712312.

It is not a de Polignac number, because 21321729 - 2⁹ = 21321217 is a prime.

It is a super-2 number, since 2×21321729² = 909232255098882, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21321709) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 6997 + ... + 9570.

It is an arithmetic number, because the mean of its divisors is an integer number (1507688).

Almost surely, 2^21321729 is an apocalyptic number.

It is an amenable number.

21321729 is a deficient number, since it is larger than the sum of its proper divisors (14862783).

21321729 is a wasteful number, since it uses less digits than its factorization.

21321729 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16597 (or 16594 counting only the distinct ones).

The product of its digits is 1512, while the sum is 27.

The square root of 21321729 is about 4617.5457767087. The cubic root of 21321729 is about 277.2942131486.

The spelling of 21321729 in words is "twenty-one million, three hundred twenty-one thousand, seven hundred twenty-nine".