21029721 has 16 divisors (see below), whose sum is σ = 28742400. Its totient is φ = 13673088.

The previous prime is 21029719. The next prime is 21029741. The reversal of 21029721 is 12792012.

It is not a de Polignac number, because 21029721 - 2¹ = 21029719 is a prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21029691 and 21029700.

It is not an unprimeable number, because it can be changed into a prime (21029741) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 20595 + ... + 21591.

It is an arithmetic number, because the mean of its divisors is an integer number (1796400).

Almost surely, 2^21029721 is an apocalyptic number.

It is an amenable number.

21029721 is a deficient number, since it is larger than the sum of its proper divisors (7712679).

21029721 is an equidigital number, since it uses as much as digits as its factorization.

21029721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1168.

The product of its (nonzero) digits is 504, while the sum is 24.

The square root of 21029721 is about 4585.8173753432. The cubic root of 21029721 is about 276.0225118164.

The spelling of 21029721 in words is "twenty-one million, twenty-nine thousand, seven hundred twenty-one".