21617664 has 88 divisors (see below), whose sum is σ = 59739648. Its totient is φ = 6942720.

The previous prime is 21617663. The next prime is 21617671. The reversal of 21617664 is 46671612.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21617663) 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, 95119 + ... + 95345.

Almost surely, 2^21617664 is an apocalyptic number.

21617664 is a gapful number since it is divisible by the number (24) 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 21617664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29869824).

21617664 is an abundant number, since it is smaller than the sum of its proper divisors (38121984).

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

21617664 is a wasteful number, since it uses less digits than its factorization.

21617664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 281 (or 263 counting only the distinct ones).

The product of its digits is 12096, while the sum is 33.

The square root of 21617664 is about 4649.4799709215. The cubic root of 21617664 is about 278.5712250961.

The spelling of 21617664 in words is "twenty-one million, six hundred seventeen thousand, six hundred sixty-four".