21002709 has 32 divisors (see below), whose sum is σ = 34836480. Its totient is φ = 10959552.

The previous prime is 21002689. The next prime is 21002711. The reversal of 21002709 is 90720012.

It is a happy number.

It is not a de Polignac number, because 21002709 - 2⁵ = 21002677 is a prime.

It is a super-2 number, since 2×21002709² = 882227570677362, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21002789) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 28852 + ... + 29570.

It is an arithmetic number, because the mean of its divisors is an integer number (1088640).

Almost surely, 2^21002709 is an apocalyptic number.

It is an amenable number.

21002709 is a deficient number, since it is larger than the sum of its proper divisors (13833771).

21002709 is a wasteful number, since it uses less digits than its factorization.

21002709 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 849.

The product of its (nonzero) digits is 252, while the sum is 21.

The square root of 21002709 is about 4582.8712615564. The cubic root of 21002709 is about 275.9042805020.

The spelling of 21002709 in words is "twenty-one million, two thousand, seven hundred nine".