21090740 has 48 divisors (see below), whose sum is σ = 49641984. Its totient is φ = 7459200.

The previous prime is 21090731. The next prime is 21090791. The reversal of 21090740 is 4709012.

It is a congruent number.

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 15 ways as a sum of consecutive naturals, for example, 6845 + ... + 9435.

It is an arithmetic number, because the mean of its divisors is an integer number (1034208).

Almost surely, 2^21090740 is an apocalyptic number.

21090740 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21090740, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24820992).

21090740 is an abundant number, since it is smaller than the sum of its proper divisors (28551244).

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

21090740 is a wasteful number, since it uses less digits than its factorization.

21090740 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2648 (or 2646 counting only the distinct ones).

The product of its (nonzero) digits is 504, while the sum is 23.

The square root of 21090740 is about 4592.4655687332. The cubic root of 21090740 is about 276.2892193316.

Adding to 21090740 its reverse (4709012), we get a palindrome (25799752).

The spelling of 21090740 in words is "twenty-one million, ninety thousand, seven hundred forty".