21609216 has 108 divisors (see below), whose sum is σ = 63613368. Its totient is φ = 7053312.

The previous prime is 21609209. The next prime is 21609223. The reversal of 21609216 is 61290612.

It is an interprime number because it is at equal distance from previous prime (21609209) and next prime (21609223).

It is a super-2 number, since 2×21609216² = 933916432269312, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21609216.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 191176 + ... + 191288.

Almost surely, 2^21609216 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 21609216, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31806684).

21609216 is an abundant number, since it is smaller than the sum of its proper divisors (42004152).

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

21609216 is a wasteful number, since it uses less digits than its factorization.

21609216 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 218 (or 201 counting only the distinct ones).

The product of its (nonzero) digits is 1296, while the sum is 27.

The square root of 21609216 is about 4648.5713934498. The cubic root of 21609216 is about 278.5349326096.

Adding to 21609216 its reverse (61290612), we get a palindrome (82899828).

The spelling of 21609216 in words is "twenty-one million, six hundred nine thousand, two hundred sixteen".