21399990 has 32 divisors (see below), whose sum is σ = 51528960. Its totient is φ = 5687904.

The previous prime is 21399979. The next prime is 21400003. The reversal of 21399990 is 9999312.

It is a happy number.

It is a congruent number.

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, 9777 + ... + 11763.

It is an arithmetic number, because the mean of its divisors is an integer number (1610280).

Almost surely, 2^21399990 is an apocalyptic number.

21399990 is an abundant number, since it is smaller than the sum of its proper divisors (30128970).

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

21399990 is a wasteful number, since it uses less digits than its factorization.

21399990 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2356.

The product of its (nonzero) digits is 39366, while the sum is 42.

The square root of 21399990 is about 4626.0123216438. The cubic root of 21399990 is about 277.6330666095.

The spelling of 21399990 in words is "twenty-one million, three hundred ninety-nine thousand, nine hundred ninety".