21351040 has 64 divisors (see below), whose sum is σ = 51854760. Its totient is φ = 8404992.

The previous prime is 21351017. The next prime is 21351053. The reversal of 21351040 is 4015312.

It can be written as a sum of positive squares in 4 ways, for example, as 20286016 + 1065024 = 4504^2 + 1032^2 .

It is a tau number, because it is divible by the number of its divisors (64).

It is a Harshad number since it is a multiple of its sum of digits (16).

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 46492 + ... + 46948.

Almost surely, 2^21351040 is an apocalyptic number.

21351040 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 21351040, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25927380).

21351040 is an abundant number, since it is smaller than the sum of its proper divisors (30503720).

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

21351040 is an equidigital number, since it uses as much as digits as its factorization.

21351040 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 549 (or 537 counting only the distinct ones).

The product of its (nonzero) digits is 120, while the sum is 16.

The square root of 21351040 is about 4620.7185588391. The cubic root of 21351040 is about 277.4212205019.

Adding to 21351040 its reverse (4015312), we get a palindrome (25366352).

The spelling of 21351040 in words is "twenty-one million, three hundred fifty-one thousand, forty".