21663210 has 32 divisors (see below), whose sum is σ = 52166592. Its totient is φ = 5757440.

The previous prime is 21663209. The next prime is 21663227. The reversal of 21663210 is 1236612.

It is a happy number.

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 15 ways as a sum of consecutive naturals, for example, 9370 + ... + 11450.

It is an arithmetic number, because the mean of its divisors is an integer number (1630206).

Almost surely, 2^21663210 is an apocalyptic number.

21663210 is an abundant number, since it is smaller than the sum of its proper divisors (30503382).

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

21663210 is a wasteful number, since it uses less digits than its factorization.

21663210 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2438.

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

The square root of 21663210 is about 4654.3753608836. The cubic root of 21663210 is about 278.7667273304.

Adding to 21663210 its reverse (1236612), we get a palindrome (22899822).

The spelling of 21663210 in words is "twenty-one million, six hundred sixty-three thousand, two hundred ten".