21621306 has 16 divisors (see below), whose sum is σ = 49420224. Its totient is φ = 6177504.

The previous prime is 21621293. The next prime is 21621329. The reversal of 21621306 is 60312612.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 257355 + ... + 257438.

It is an arithmetic number, because the mean of its divisors is an integer number (3088764).

Almost surely, 2^21621306 is an apocalyptic number.

21621306 is an abundant number, since it is smaller than the sum of its proper divisors (27798918).

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

21621306 is a wasteful number, since it uses less digits than its factorization.

21621306 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 514805.

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

The square root of 21621306 is about 4649.8716111308. The cubic root of 21621306 is about 278.5868681590.

Adding to 21621306 its reverse (60312612), we get a palindrome (81933918).

The spelling of 21621306 in words is "twenty-one million, six hundred twenty-one thousand, three hundred six".