21390450 has 48 divisors (see below), whose sum is σ = 53969760. Its totient is φ = 5605120.

The previous prime is 21390449. The next prime is 21390461. The reversal of 21390450 is 5409312.

It is a self number, because there is not a number n which added to its sum of digits gives 21390450.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 7642 + ... + 10058.

It is an arithmetic number, because the mean of its divisors is an integer number (1124370).

Almost surely, 2^21390450 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21390450, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26984880).

21390450 is an abundant number, since it is smaller than the sum of its proper divisors (32579310).

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

21390450 is a wasteful number, since it uses less digits than its factorization.

21390450 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2491 (or 2486 counting only the distinct ones).

The product of its (nonzero) digits is 1080, while the sum is 24.

The square root of 21390450 is about 4624.9810810424. The cubic root of 21390450 is about 277.5918047034.

Adding to 21390450 its reverse (5409312), we get a palindrome (26799762).

The spelling of 21390450 in words is "twenty-one million, three hundred ninety thousand, four hundred fifty".