21731616 has 72 divisors (see below), whose sum is σ = 62863164. Its totient is φ = 7119360.

The previous prime is 21731597. The next prime is 21731621. The reversal of 21731616 is 61613712.

21731616 is a `hidden beast` number, since 2 + 17 + 31 + 616 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 21123216 + 608400 = 4596^2 + 780^2 .

It is a tau number, because it is divible by the number of its divisors (72).

It is a self number, because there is not a number n which added to its sum of digits gives 21731616.

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, 16950 + ... + 18186.

Almost surely, 2^21731616 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 21731616, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31431582).

21731616 is an abundant number, since it is smaller than the sum of its proper divisors (41131548).

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

21731616 is a wasteful number, since it uses less digits than its factorization.

21731616 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1314 (or 1303 counting only the distinct ones).

The product of its digits is 1512, while the sum is 27.

The square root of 21731616 is about 4661.7181381975. The cubic root of 21731616 is about 279.0598399414.

The spelling of 21731616 in words is "twenty-one million, seven hundred thirty-one thousand, six hundred sixteen".