21290640 has 320 divisors, whose sum is σ = 85708800. Its totient is φ = 4257792.

The previous prime is 21290629. The next prime is 21290641. The reversal of 21290640 is 4609212.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a self number, because there is not a number n which added to its sum of digits gives 21290640.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21290641) by changing a digit.

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 63 ways as a sum of consecutive naturals, for example, 734146 + ... + 734174.

It is an arithmetic number, because the mean of its divisors is an integer number (267840).

Almost surely, 2^21290640 is an apocalyptic number.

21290640 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 21290640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (42854400).

21290640 is an abundant number, since it is smaller than the sum of its proper divisors (64418160).

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

21290640 is a wasteful number, since it uses less digits than its factorization.

21290640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 94 (or 88 counting only the distinct ones).

The product of its (nonzero) digits is 864, while the sum is 24.

The square root of 21290640 is about 4614.1781500068. The cubic root of 21290640 is about 277.1593742845.

Adding to 21290640 its reverse (4609212), we get a palindrome (25899852).

The spelling of 21290640 in words is "twenty-one million, two hundred ninety thousand, six hundred forty".