21521370 has 64 divisors (see below), whose sum is σ = 56165760. Its totient is φ = 5246208.

The previous prime is 21521369. The next prime is 21521387. The reversal of 21521370 is 7312512.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 54012 + ... + 54408.

It is an arithmetic number, because the mean of its divisors is an integer number (877590).

Almost surely, 2^21521370 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21521370, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28082880).

21521370 is an abundant number, since it is smaller than the sum of its proper divisors (34644390).

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

21521370 is a wasteful number, since it uses less digits than its factorization.

21521370 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 559.

The product of its (nonzero) digits is 420, while the sum is 21.

The square root of 21521370 is about 4639.1130617824. The cubic root of 21521370 is about 278.1569856746.

Adding to 21521370 its reverse (7312512), we get a palindrome (28833882).

The spelling of 21521370 in words is "twenty-one million, five hundred twenty-one thousand, three hundred seventy".