21801390 has 32 divisors (see below), whose sum is σ = 56349216. Its totient is φ = 5366400.

The previous prime is 21801383. The next prime is 21801407. The reversal of 21801390 is 9310812.

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 21801390.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 27561 + ... + 28340.

It is an arithmetic number, because the mean of its divisors is an integer number (1760913).

Almost surely, 2^21801390 is an apocalyptic number.

21801390 is an abundant number, since it is smaller than the sum of its proper divisors (34547826).

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

21801390 is a wasteful number, since it uses less digits than its factorization.

21801390 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 55924.

The product of its (nonzero) digits is 432, while the sum is 24.

The square root of 21801390 is about 4669.1958622444. The cubic root of 21801390 is about 279.3581813016.

It can be divided in two parts, 2180 and 1390, that added together give a triangular number (3570 = T₈₄).

The spelling of 21801390 in words is "twenty-one million, eight hundred one thousand, three hundred ninety".