21355290 has 144 divisors (see below), whose sum is σ = 63862344. Its totient is φ = 4942080.

The previous prime is 21355289. The next prime is 21355291. The reversal of 21355290 is 9255312.

21355290 is a `hidden beast` number, since 2 + 135 + 529 + 0 = 666.

It is an interprime number because it is at equal distance from previous prime (21355289) and next prime (21355291).

It can be written as a sum of positive squares in 4 ways, for example, as 21040569 + 314721 = 4587^2 + 561^2 .

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21355291) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 402904 + ... + 402956.

Almost surely, 2^21355290 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21355290, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31931172).

21355290 is an abundant number, since it is smaller than the sum of its proper divisors (42507054).

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

21355290 is a wasteful number, since it uses less digits than its factorization.

21355290 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 125 (or 111 counting only the distinct ones).

The product of its (nonzero) digits is 2700, while the sum is 27.

The square root of 21355290 is about 4621.1784211389. The cubic root of 21355290 is about 277.4396265056.

The spelling of 21355290 in words is "twenty-one million, three hundred fifty-five thousand, two hundred ninety".