21717072 has 100 divisors (see below), whose sum is σ = 67743060. Its totient is φ = 6676992.

The previous prime is 21717071. The next prime is 21717089. The reversal of 21717072 is 27071712.

It can be written as a sum of positive squares in 2 ways, for example, as 10265616 + 11451456 = 3204^2 + 3384^2 .

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21717071) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 16204 + ... + 17492.

Almost surely, 2^21717072 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 21717072, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33871530).

21717072 is an abundant number, since it is smaller than the sum of its proper divisors (46025988).

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

21717072 is a wasteful number, since it uses less digits than its factorization.

21717072 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1322 (or 1307 counting only the distinct ones).

The product of its (nonzero) digits is 1372, while the sum is 27.

The square root of 21717072 is about 4660.1579372377. The cubic root of 21717072 is about 278.9975719525.

Adding to 21717072 its reverse (27071712), we get a palindrome (48788784).

The spelling of 21717072 in words is "twenty-one million, seven hundred seventeen thousand, seventy-two".