21787920 has 320 divisors, whose sum is σ = 94279680. Its totient is φ = 4492800.

The previous prime is 21787907. The next prime is 21787939. The reversal of 21787920 is 2978712.

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

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

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 166255 + ... + 166385.

It is an arithmetic number, because the mean of its divisors is an integer number (294624).

Almost surely, 2^21787920 is an apocalyptic number.

21787920 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 21787920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (47139840).

21787920 is an abundant number, since it is smaller than the sum of its proper divisors (72491760).

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

21787920 is a wasteful number, since it uses less digits than its factorization.

21787920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 171 (or 159 counting only the distinct ones).

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

The square root of 21787920 is about 4667.7532068437. The cubic root of 21787920 is about 279.3006355832.

The spelling of 21787920 in words is "twenty-one million, seven hundred eighty-seven thousand, nine hundred twenty".