21505050 has 72 divisors (see below), whose sum is σ = 66040416. Its totient is φ = 4914720.

The previous prime is 21505039. The next prime is 21505063. The reversal of 21505050 is 5050512.

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

21505050 is a modest number, since divided by 5050 gives 2150 as remainder.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 264 + ... + 6563.

It is an arithmetic number, because the mean of its divisors is an integer number (917228).

Almost surely, 2^21505050 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21505050, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33020208).

21505050 is an abundant number, since it is smaller than the sum of its proper divisors (44535366).

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

21505050 is a wasteful number, since it uses less digits than its factorization.

21505050 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6852 (or 6844 counting only the distinct ones).

The product of its (nonzero) digits is 250, while the sum is 18.

The square root of 21505050 is about 4637.3537712795. The cubic root of 21505050 is about 278.0866575936.

Adding to 21505050 its reverse (5050512), we get a palindrome (26555562).

The spelling of 21505050 in words is "twenty-one million, five hundred five thousand, fifty".