21288258 has 64 divisors (see below), whose sum is σ = 49751040. Its totient is φ = 6823440.

The previous prime is 21288221. The next prime is 21288259. The reversal of 21288258 is 85288212.

It is a happy number.

It is not an unprimeable number, because it can be changed into a prime (21288259) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 135516 + ... + 135672.

It is an arithmetic number, because the mean of its divisors is an integer number (777360).

Almost surely, 2^21288258 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21288258, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24875520).

21288258 is an abundant number, since it is smaller than the sum of its proper divisors (28462782).

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

21288258 is an equidigital number, since it uses as much as digits as its factorization.

21288258 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 211 (or 193 counting only the distinct ones).

The product of its digits is 20480, while the sum is 36.

The square root of 21288258 is about 4613.9200253147. The cubic root of 21288258 is about 277.1490376882.

The spelling of 21288258 in words is "twenty-one million, two hundred eighty-eight thousand, two hundred fifty-eight".