21390616 has 32 divisors (see below), whose sum is σ = 43696800. Its totient is φ = 9757440.

The previous prime is 21390613. The next prime is 21390617. The reversal of 21390616 is 61609312.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21390613) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 8101 + ... + 10411.

It is an arithmetic number, because the mean of its divisors is an integer number (1365525).

Almost surely, 2^21390616 is an apocalyptic number.

21390616 is a gapful number since it is divisible by the number (26) 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 21390616, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21848400).

21390616 is an abundant number, since it is smaller than the sum of its proper divisors (22306184).

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

21390616 is a wasteful number, since it uses less digits than its factorization.

21390616 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2419 (or 2415 counting only the distinct ones).

The product of its (nonzero) digits is 1944, while the sum is 28.

The square root of 21390616 is about 4624.9990270269. Note that the first 3 decimals coincide. The cubic root of 21390616 is about 277.5925227828.

Adding to 21390616 its reverse (61609312), we get a palindrome (82999928).

The spelling of 21390616 in words is "twenty-one million, three hundred ninety thousand, six hundred sixteen".