21506550 has 96 divisors (see below), whose sum is σ = 59058720. Its totient is φ = 5145600.

The previous prime is 21506533. The next prime is 21506593. The reversal of 21506550 is 5560512.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21506550.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 79816 + ... + 80084.

It is an arithmetic number, because the mean of its divisors is an integer number (615195).

Almost surely, 2^21506550 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21506550, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29529360).

21506550 is an abundant number, since it is smaller than the sum of its proper divisors (37552170).

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

21506550 is a wasteful number, since it uses less digits than its factorization.

21506550 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 338 (or 333 counting only the distinct ones).

The product of its (nonzero) digits is 1500, while the sum is 24.

The square root of 21506550 is about 4637.5154986264. The cubic root of 21506550 is about 278.0931230562.

The spelling of 21506550 in words is "twenty-one million, five hundred six thousand, five hundred fifty".