21155100 has 72 divisors (see below), whose sum is σ = 61746048. Its totient is φ = 5592000.

The previous prime is 21155087. The next prime is 21155107. The reversal of 21155100 is 155112.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a self number, because there is not a number n which added to its sum of digits gives 21155100.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21155107) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 45067 + ... + 45533.

It is an arithmetic number, because the mean of its divisors is an integer number (857584).

Almost surely, 2^21155100 is an apocalyptic number.

21155100 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 21155100, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30873024).

21155100 is an abundant number, since it is smaller than the sum of its proper divisors (40590948).

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

21155100 is a wasteful number, since it uses less digits than its factorization.

21155100 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 635 (or 628 counting only the distinct ones).

The product of its (nonzero) digits is 50, while the sum is 15.

The square root of 21155100 is about 4599.4673604669. The cubic root of 21155100 is about 276.5699731454.

The spelling of 21155100 in words is "twenty-one million, one hundred fifty-five thousand, one hundred".