21665028 has 48 divisors (see below), whose sum is σ = 63028224. Its totient is φ = 5627040.

The previous prime is 21665009. The next prime is 21665041. The reversal of 21665028 is 82056612.

It is a junction number, because it is equal to n+sod(n) for n = 21664986 and 21665004.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 10800 + ... + 12647.

It is an arithmetic number, because the mean of its divisors is an integer number (1313088).

Almost surely, 2^21665028 is an apocalyptic number.

21665028 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

21665028 is an abundant number, since it is smaller than the sum of its proper divisors (41363196).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21665028 is a wasteful number, since it uses less digits than its factorization.

21665028 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23472 (or 23470 counting only the distinct ones).

The product of its (nonzero) digits is 5760, while the sum is 30.

The square root of 21665028 is about 4654.5706568920. The cubic root of 21665028 is about 278.7745252473.

The spelling of 21665028 in words is "twenty-one million, six hundred sixty-five thousand, twenty-eight".