21155550 has 96 divisors (see below), whose sum is σ = 59579520. Its totient is φ = 4924800.

The previous prime is 21155543. The next prime is 21155551. The reversal of 21155550 is 5555112.

It is a self number, because there is not a number n which added to its sum of digits gives 21155550.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21155551) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 36765 + ... + 37335.

It is an arithmetic number, because the mean of its divisors is an integer number (620620).

Almost surely, 2^21155550 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21155550, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29789760).

21155550 is an abundant number, since it is smaller than the sum of its proper divisors (38423970).

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

21155550 is a wasteful number, since it uses less digits than its factorization.

21155550 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 618 (or 613 counting only the distinct ones).

The product of its (nonzero) digits is 1250, while the sum is 24.

The square root of 21155550 is about 4599.5162789146. The cubic root of 21155550 is about 276.5719341478.

The spelling of 21155550 in words is "twenty-one million, one hundred fifty-five thousand, five hundred fifty".