21987420 has 96 divisors (see below), whose sum is σ = 75790848. Its totient is φ = 4637952.

The previous prime is 21987403. The next prime is 21987461. The reversal of 21987420 is 2478912.

It is a happy number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 3447 + ... + 7473.

It is an arithmetic number, because the mean of its divisors is an integer number (789488).

Almost surely, 2^21987420 is an apocalyptic number.

21987420 is a gapful number since it is divisible by the number (20) 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 21987420, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37895424).

21987420 is an abundant number, since it is smaller than the sum of its proper divisors (53803428).

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

21987420 is a wasteful number, since it uses less digits than its factorization.

21987420 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4059 (or 4057 counting only the distinct ones).

The product of its (nonzero) digits is 8064, while the sum is 33.

The square root of 21987420 is about 4689.0745355560. The cubic root of 21987420 is about 280.1505143145.

The spelling of 21987420 in words is "twenty-one million, nine hundred eighty-seven thousand, four hundred twenty".