21987028 has 48 divisors (see below), whose sum is σ = 47582080. Its totient is φ = 8678016.

The previous prime is 21987019. The next prime is 21987041. The reversal of 21987028 is 82078912.

It is a super-4 number, since 4×21987028⁴ (a number of 30 digits) contains 4444 as substring.

It is a Harshad number since it is a multiple of its sum of digits (37).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 19126 + ... + 20242.

Almost surely, 2^21987028 is an apocalyptic number.

21987028 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21987028, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23791040).

21987028 is an abundant number, since it is smaller than the sum of its proper divisors (25595052).

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

21987028 is a wasteful number, since it uses less digits than its factorization.

21987028 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1184 (or 1182 counting only the distinct ones).

The product of its (nonzero) digits is 16128, while the sum is 37.

The square root of 21987028 is about 4689.0327360768. The cubic root of 21987028 is about 280.1488494283.

The spelling of 21987028 in words is "twenty-one million, nine hundred eighty-seven thousand, twenty-eight".