21002400 has 108 divisors (see below), whose sum is σ = 74085102. Its totient is φ = 5598720.

The previous prime is 21002393. The next prime is 21002413. The reversal of 21002400 is 420012.

It can be written as a sum of positive squares in 3 ways, for example, as 20466576 + 535824 = 4524^2 + 732^2 .

It is a super-2 number, since 2×21002400² = 882201611520000, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (9).

It is an unprimeable number.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 5742 + ... + 8658.

Almost surely, 2^21002400 is an apocalyptic number.

21002400 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 21002400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37042551).

21002400 is an abundant number, since it is smaller than the sum of its proper divisors (53082702).

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

21002400 is a wasteful number, since it uses less digits than its factorization.

21002400 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2943 (or 2927 counting only the distinct ones).

The product of its (nonzero) digits is 16, while the sum is 9.

The square root of 21002400 is about 4582.8375489428. The cubic root of 21002400 is about 275.9029274251.

Adding to 21002400 its reverse (420012), we get a palindrome (21422412).

The spelling of 21002400 in words is "twenty-one million, two thousand, four hundred".