21011664 has 20 divisors (see below), whose sum is σ = 54280256. Its totient is φ = 7003872.

The previous prime is 21011659. The next prime is 21011693. The reversal of 21011664 is 46611012.

It is a self number, because there is not a number n which added to its sum of digits gives 21011664.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 218824 + ... + 218919.

Almost surely, 2^21011664 is an apocalyptic number.

21011664 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21011664 is an abundant number, since it is smaller than the sum of its proper divisors (33268592).

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

21011664 is a wasteful number, since it uses less digits than its factorization.

21011664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 437754 (or 437748 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 21.

The square root of 21011664 is about 4583.8481650247. The cubic root of 21011664 is about 275.9434876945.

Adding to 21011664 its reverse (46611012), we get a palindrome (67622676).

The spelling of 21011664 in words is "twenty-one million, eleven thousand, six hundred sixty-four".