21309916 has 12 divisors (see below), whose sum is σ = 37427040. Its totient is φ = 10616480.

The previous prime is 21309913. The next prime is 21309973. The reversal of 21309916 is 61990312.

It is a super-2 number, since 2×21309916² = 908225039854112, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21309913) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8356 + ... + 10603.

It is an arithmetic number, because the mean of its divisors is an integer number (3118920).

Almost surely, 2^21309916 is an apocalyptic number.

It is an amenable number.

21309916 is a deficient number, since it is larger than the sum of its proper divisors (16117124).

21309916 is a wasteful number, since it uses less digits than its factorization.

21309916 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19244 (or 19242 counting only the distinct ones).

The product of its (nonzero) digits is 2916, while the sum is 31.

The square root of 21309916 is about 4616.2664567808. The cubic root of 21309916 is about 277.2429933863.

The spelling of 21309916 in words is "twenty-one million, three hundred nine thousand, nine hundred sixteen".