21521420 has 48 divisors (see below), whose sum is σ = 46986240. Its totient is φ = 8273664.

The previous prime is 21521419. The next prime is 21521431. The reversal of 21521420 is 2412512.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 93866 + ... + 94094.

It is an arithmetic number, because the mean of its divisors is an integer number (978880).

Almost surely, 2^21521420 is an apocalyptic number.

21521420 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 21521420, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23493120).

21521420 is an abundant number, since it is smaller than the sum of its proper divisors (25464820).

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

21521420 is a wasteful number, since it uses less digits than its factorization.

21521420 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 402 (or 400 counting only the distinct ones).

The product of its (nonzero) digits is 160, while the sum is 17.

The square root of 21521420 is about 4639.1184507404. The cubic root of 21521420 is about 278.1572010858.

Adding to 21521420 its reverse (2412512), we get a palindrome (23933932).

The spelling of 21521420 in words is "twenty-one million, five hundred twenty-one thousand, four hundred twenty".