21720790 has 32 divisors (see below), whose sum is σ = 48121920. Its totient is φ = 6873984.

The previous prime is 21720779. The next prime is 21720821. The reversal of 21720790 is 9702712.

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, 11025 + ... + 12844.

It is an arithmetic number, because the mean of its divisors is an integer number (1503810).

Almost surely, 2^21720790 is an apocalyptic number.

21720790 is an abundant number, since it is smaller than the sum of its proper divisors (26401130).

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

21720790 is a wasteful number, since it uses less digits than its factorization.

21720790 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23896.

The product of its (nonzero) digits is 1764, while the sum is 28.

The square root of 21720790 is about 4660.5568336841. The cubic root of 21720790 is about 279.0134926650.

The spelling of 21720790 in words is "twenty-one million, seven hundred twenty thousand, seven hundred ninety".