21290220 has 144 divisors (see below), whose sum is σ = 75286848. Its totient is φ = 4769280.

The previous prime is 21290219. The next prime is 21290303. The reversal of 21290220 is 2209212.

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

It is a junction number, because it is equal to n+sod(n) for n = 21290193 and 21290202.

It is a congruent number.

It is an unprimeable number.

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 47 ways as a sum of consecutive naturals, for example, 76722 + ... + 76998.

Almost surely, 2^21290220 is an apocalyptic number.

21290220 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 21290220, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37643424).

21290220 is an abundant number, since it is smaller than the sum of its proper divisors (53996628).

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

21290220 is a wasteful number, since it uses less digits than its factorization.

21290220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 360 (or 355 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 18.

The square root of 21290220 is about 4614.1326378855. The cubic root of 21290220 is about 277.1575517668.

Adding to 21290220 its reverse (2209212), we get a palindrome (23499432).

The spelling of 21290220 in words is "twenty-one million, two hundred ninety thousand, two hundred twenty".