21000400 has 30 divisors (see below), whose sum is σ = 50454422. Its totient is φ = 8400000.

The previous prime is 21000391. The next prime is 21000407. The reversal of 21000400 is 400012.

It can be written as a sum of positive squares in 3 ways, for example, as 425104 + 20575296 = 652^2 + 4536^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21000407) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 25851 + ... + 26650.

Almost surely, 2^21000400 is an apocalyptic number.

21000400 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21000400 is an abundant number, since it is smaller than the sum of its proper divisors (29454022).

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

21000400 is a wasteful number, since it uses less digits than its factorization.

21000400 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 52519 (or 52508 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 7.

The square root of 21000400 is about 4582.6193383261. The cubic root of 21000400 is about 275.8941693249.

Adding to 21000400 its reverse (400012), we get a palindrome (21400412).

The spelling of 21000400 in words is "twenty-one million, four hundred", and thus it is an aban number.