21987072 has 72 divisors (see below), whose sum is σ = 65040080. Its totient is φ = 7326720.

The previous prime is 21987071. The next prime is 21987073. The reversal of 21987072 is 27078912.

It is an interprime number because it is at equal distance from previous prime (21987071) and next prime (21987073).

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

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a nialpdrome in base 12.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21987071) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5322 + ... + 8502.

Almost surely, 2^21987072 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 21987072, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32520040).

21987072 is an abundant number, since it is smaller than the sum of its proper divisors (43053008).

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

21987072 is an equidigital number, since it uses as much as digits as its factorization.

21987072 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3206 (or 3186 counting only the distinct ones).

The product of its (nonzero) digits is 14112, while the sum is 36.

The square root of 21987072 is about 4689.0374278737. The cubic root of 21987072 is about 280.1490363043.

The spelling of 21987072 in words is "twenty-one million, nine hundred eighty-seven thousand, seventy-two".