21216390 has 32 divisors (see below), whose sum is σ = 54837216. Its totient is φ = 5222400.

The previous prime is 21216389. The next prime is 21216401. The reversal of 21216390 is 9361212.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21216390.

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, 26811 + ... + 27590.

It is an arithmetic number, because the mean of its divisors is an integer number (1713663).

Almost surely, 2^21216390 is an apocalyptic number.

21216390 is an abundant number, since it is smaller than the sum of its proper divisors (33620826).

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

21216390 is a wasteful number, since it uses less digits than its factorization.

21216390 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 54424.

The product of its (nonzero) digits is 648, while the sum is 24.

The square root of 21216390 is about 4606.1252696817. The cubic root of 21216390 is about 276.8368060444.

The spelling of 21216390 in words is "twenty-one million, two hundred sixteen thousand, three hundred ninety".