21316640 has 72 divisors (see below), whose sum is σ = 53613252. Its totient is φ = 8007680.

The previous prime is 21316639. The next prime is 21316643. The reversal of 21316640 is 4661312.

It is a happy number.

It can be written as a sum of positive squares in 6 ways, for example, as 13454224 + 7862416 = 3668^2 + 2804^2 .

It is not an unprimeable number, because it can be changed into a prime (21316643) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 46010 + ... + 46470.

Almost surely, 2^21316640 is an apocalyptic number.

21316640 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 21316640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26806626).

21316640 is an abundant number, since it is smaller than the sum of its proper divisors (32296612).

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

21316640 is a wasteful number, since it uses less digits than its factorization.

21316640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 510 (or 485 counting only the distinct ones).

The product of its (nonzero) digits is 864, while the sum is 23.

The square root of 21316640 is about 4616.9946935209. The cubic root of 21316640 is about 277.2721501702.

Adding to 21316640 its reverse (4661312), we get a palindrome (25977952).

The spelling of 21316640 in words is "twenty-one million, three hundred sixteen thousand, six hundred forty".