21387520 has 216 divisors, whose sum is σ = 67108608. Its totient is φ = 6451200.

The previous prime is 21387511. The next prime is 21387557. The reversal of 21387520 is 2578312.

It is a Harshad number since it is a multiple of its sum of digits (28).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 689905 + ... + 689935.

It is an arithmetic number, because the mean of its divisors is an integer number (310688).

Almost surely, 2^21387520 is an apocalyptic number.

21387520 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 21387520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33554304).

21387520 is an abundant number, since it is smaller than the sum of its proper divisors (45721088).

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

21387520 is a wasteful number, since it uses less digits than its factorization.

21387520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 77 (or 56 counting only the distinct ones).

The product of its (nonzero) digits is 3360, while the sum is 28.

The square root of 21387520 is about 4624.6643121420. The cubic root of 21387520 is about 277.5791295590.

The spelling of 21387520 in words is "twenty-one million, three hundred eighty-seven thousand, five hundred twenty".