21691816 has 32 divisors (see below), whose sum is σ = 42900480. Its totient is φ = 10267200.

The previous prime is 21691793. The next prime is 21691843. The reversal of 21691816 is 61819612.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10726 + ... + 12586.

It is an arithmetic number, because the mean of its divisors is an integer number (1340640).

Almost surely, 2^21691816 is an apocalyptic number.

It is an amenable number.

21691816 is a deficient number, since it is larger than the sum of its proper divisors (21208664).

21691816 is a wasteful number, since it uses less digits than its factorization.

21691816 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1945 (or 1941 counting only the distinct ones).

The product of its digits is 5184, while the sum is 34.

The square root of 21691816 is about 4657.4473695362. The cubic root of 21691816 is about 278.8893760290.

The spelling of 21691816 in words is "twenty-one million, six hundred ninety-one thousand, eight hundred sixteen".