21688290 has 128 divisors (see below), whose sum is σ = 64350720. Its totient is φ = 5163264.

The previous prime is 21688283. The next prime is 21688301. The reversal of 21688290 is 9288612.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 129787 + ... + 129953.

It is an arithmetic number, because the mean of its divisors is an integer number (502740).

Almost surely, 2^21688290 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21688290, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32175360).

21688290 is an abundant number, since it is smaller than the sum of its proper divisors (42662430).

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

21688290 is a wasteful number, since it uses less digits than its factorization.

21688290 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 233 (or 227 counting only the distinct ones).

The product of its (nonzero) digits is 13824, while the sum is 36.

The square root of 21688290 is about 4657.0688206210. The cubic root of 21688290 is about 278.8742640743.

The spelling of 21688290 in words is "twenty-one million, six hundred eighty-eight thousand, two hundred ninety".