21390290 has 16 divisors (see below), whose sum is σ = 38577600. Its totient is φ = 8539440.

The previous prime is 21390289. The next prime is 21390337. The reversal of 21390290 is 9209312.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4205 + ... + 7775.

It is an arithmetic number, because the mean of its divisors is an integer number (2411100).

Almost surely, 2^21390290 is an apocalyptic number.

21390290 is a deficient number, since it is larger than the sum of its proper divisors (17187310).

21390290 is a wasteful number, since it uses less digits than its factorization.

21390290 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4177.

The product of its (nonzero) digits is 972, while the sum is 26.

The square root of 21390290 is about 4624.9637836420. The cubic root of 21390290 is about 277.5911125753.

The spelling of 21390290 in words is "twenty-one million, three hundred ninety thousand, two hundred ninety".