21399890 has 64 divisors (see below), whose sum is σ = 43545600. Its totient is φ = 7533504.

The previous prime is 21399839. The next prime is 21399901. The reversal of 21399890 is 9899312.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 257789 + ... + 257871.

It is an arithmetic number, because the mean of its divisors is an integer number (680400).

Almost surely, 2^21399890 is an apocalyptic number.

21399890 is an abundant number, since it is smaller than the sum of its proper divisors (22145710).

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

21399890 is a wasteful number, since it uses less digits than its factorization.

21399890 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 191.

The product of its (nonzero) digits is 34992, while the sum is 41.

The square root of 21399890 is about 4626.0015131861. The cubic root of 21399890 is about 277.6326341584.

The spelling of 21399890 in words is "twenty-one million, three hundred ninety-nine thousand, eight hundred ninety".