21665635400 has 96 divisors (see below), whose sum is σ = 53068478400. Its totient is φ = 8203219200.

The previous prime is 21665635367. The next prime is 21665635417. The reversal of 21665635400 is 453656612.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (38).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 8134469 + ... + 8137131.

It is an arithmetic number, because the mean of its divisors is an integer number (552796650).

Almost surely, 2^21665635400 is an apocalyptic number.

21665635400 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 21665635400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26534239200).

21665635400 is an abundant number, since it is smaller than the sum of its proper divisors (31402843000).

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

21665635400 is a wasteful number, since it uses less digits than its factorization.

21665635400 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4839 (or 4830 counting only the distinct ones).

The product of its (nonzero) digits is 129600, while the sum is 38.

The spelling of 21665635400 in words is "twenty-one billion, six hundred sixty-five million, six hundred thirty-five thousand, four hundred".