21617816 has 32 divisors (see below), whose sum is σ = 44513280. Its totient is φ = 9760800.

The previous prime is 21617809. The next prime is 21617821. The reversal of 21617816 is 61871612.

It is a happy number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 13961 + ... + 15431.

It is an arithmetic number, because the mean of its divisors is an integer number (1391040).

Almost surely, 2^21617816 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21617816, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22256640).

21617816 is an abundant number, since it is smaller than the sum of its proper divisors (22895464).

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

21617816 is a wasteful number, since it uses less digits than its factorization.

21617816 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1655 (or 1651 counting only the distinct ones).

The product of its digits is 4032, while the sum is 32.

The square root of 21617816 is about 4649.4963168068. The cubic root of 21617816 is about 278.5718779993.

The spelling of 21617816 in words is "twenty-one million, six hundred seventeen thousand, eight hundred sixteen".