21390420 has 96 divisors (see below), whose sum is σ = 64568448. Its totient is φ = 5271552.

The previous prime is 21390389. The next prime is 21390427. The reversal of 21390420 is 2409312.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21390427) 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, 68184 + ... + 68496.

It is an arithmetic number, because the mean of its divisors is an integer number (672588).

Almost surely, 2^21390420 is an apocalyptic number.

21390420 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 21390420, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32284224).

21390420 is an abundant number, since it is smaller than the sum of its proper divisors (43178028).

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

21390420 is a wasteful number, since it uses less digits than its factorization.

21390420 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 409 (or 407 counting only the distinct ones).

The product of its (nonzero) digits is 432, while the sum is 21.

The square root of 21390420 is about 4624.9778377847. The cubic root of 21390420 is about 277.5916749297.

Adding to 21390420 its reverse (2409312), we get a palindrome (23799732).

The spelling of 21390420 in words is "twenty-one million, three hundred ninety thousand, four hundred twenty".