21717664 has 24 divisors (see below), whose sum is σ = 43485120. Its totient is φ = 10673856.

The previous prime is 21717649. The next prime is 21717667. The reversal of 21717664 is 46671712.

It is a happy number.

It is a Smith number, since the sum of its digits (34) coincides with the sum of the digits of its prime factors.

It is not an unprimeable number, because it can be changed into a prime (21717667) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3864 + ... + 7639.

It is an arithmetic number, because the mean of its divisors is an integer number (1811880).

Almost surely, 2^21717664 is an apocalyptic number.

It is an amenable number.

21717664 is an abundant number, since it is smaller than the sum of its proper divisors (21767456).

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

21717664 is a wasteful number, since it uses less digits than its factorization.

21717664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11572 (or 11564 counting only the distinct ones).

The product of its digits is 14112, while the sum is 34.

The square root of 21717664 is about 4660.2214539655. The cubic root of 21717664 is about 279.0001070558. Note that the first 3 decimals are identical.

The spelling of 21717664 in words is "twenty-one million, seven hundred seventeen thousand, six hundred sixty-four".