21506000400 has 90 divisors (see below), whose sum is σ = 74631807770. Its totient is φ = 5734932480.

The previous prime is 21506000389. The next prime is 21506000401. The reversal of 21506000400 is 400060512.

It is a happy number.

21506000400 is a `hidden beast` number, since 21 + 5 + 0 + 600 + 0 + 40 + 0 = 666.

It can be written as a sum of positive squares in 3 ways, for example, as 6230016 + 21499770384 = 2496^2 + 146628^2 .

It is a tau number, because it is divible by the number of its divisors (90).

It is a Harshad number since it is a multiple of its sum of digits (18).

It is not an unprimeable number, because it can be changed into a prime (21506000401) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 2983345 + ... + 2990544.

Almost surely, 2^21506000400 is an apocalyptic number.

21506000400 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21506000400 is an abundant number, since it is smaller than the sum of its proper divisors (53125807370).

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

21506000400 is a wasteful number, since it uses less digits than its factorization.

21506000400 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5973913 (or 5973899 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 18.

Adding to 21506000400 its reverse (400060512), we get a palindrome (21906060912).

The spelling of 21506000400 in words is "twenty-one billion, five hundred six million, four hundred", and thus it is an aban number.