21222729 has 20 divisors (see below), whose sum is σ = 34586640. Its totient is φ = 12861720.

The previous prime is 21222697. The next prime is 21222739. The reversal of 21222729 is 92722212.

It is not a de Polignac number, because 21222729 - 2⁵ = 21222697 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21222739) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 11019 + ... + 12800.

It is an arithmetic number, because the mean of its divisors is an integer number (1729332).

Almost surely, 2^21222729 is an apocalyptic number.

It is an amenable number.

21222729 is a deficient number, since it is larger than the sum of its proper divisors (13363911).

21222729 is a wasteful number, since it uses less digits than its factorization.

21222729 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23842 (or 23833 counting only the distinct ones).

The product of its digits is 2016, while the sum is 27.

The square root of 21222729 is about 4606.8133237630. The cubic root of 21222729 is about 276.8643742557.

It can be divided in two parts, 2122 and 2729, that added together give a triangular number (4851 = T₉₈).

The spelling of 21222729 in words is "twenty-one million, two hundred twenty-two thousand, seven hundred twenty-nine".