21002440 has 32 divisors (see below), whose sum is σ = 47751480. Its totient is φ = 8312832.

The previous prime is 21002431. The next prime is 21002461. The reversal of 21002440 is 4420012.

It can be written as a sum of positive squares in 4 ways, for example, as 13527684 + 7474756 = 3678^2 + 2734^2 .

It is a super-2 number, since 2×21002440² = 882204971907200, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21002440.

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, 1174 + ... + 6586.

Almost surely, 2^21002440 is an apocalyptic number.

21002440 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21002440 is an abundant number, since it is smaller than the sum of its proper divisors (26749040).

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

21002440 is a wasteful number, since it uses less digits than its factorization.

21002440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5521 (or 5517 counting only the distinct ones).

The product of its (nonzero) digits is 64, while the sum is 13.

The square root of 21002440 is about 4582.8419130492. The cubic root of 21002440 is about 275.9031025814.

Adding to 21002440 its reverse (4420012), we get a palindrome (25422452).

The spelling of 21002440 in words is "twenty-one million, two thousand, four hundred forty".