21665830 has 16 divisors (see below), whose sum is σ = 39074400. Its totient is φ = 8649472.

The previous prime is 21665827. The next prime is 21665867. The reversal of 21665830 is 3856612.

It is a junction number, because it is equal to n+sod(n) for n = 21665792 and 21665801.

It is a congruent number.

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, 4182 + ... + 7798.

It is an arithmetic number, because the mean of its divisors is an integer number (2442150).

Almost surely, 2^21665830 is an apocalyptic number.

21665830 is a deficient number, since it is larger than the sum of its proper divisors (17408570).

21665830 is a wasteful number, since it uses less digits than its factorization.

21665830 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4223.

The product of its (nonzero) digits is 8640, while the sum is 31.

The square root of 21665830 is about 4654.6568079720. The cubic root of 21665830 is about 278.7779651138. Note that the first 3 decimals are identical.

The spelling of 21665830 in words is "twenty-one million, six hundred sixty-five thousand, eight hundred thirty".