21781320 has 128 divisors (see below), whose sum is σ = 73872000. Its totient is φ = 5089280.

The previous prime is 21781303. The next prime is 21781337. The reversal of 21781320 is 2318712.

It is an interprime number because it is at equal distance from previous prime (21781303) and next prime (21781337).

It is a Harshad number since it is a multiple of its sum of digits (24).

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, 37996 + ... + 38564.

It is an arithmetic number, because the mean of its divisors is an integer number (577125).

Almost surely, 2^21781320 is an apocalyptic number.

21781320 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 21781320, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36936000).

21781320 is an abundant number, since it is smaller than the sum of its proper divisors (52090680).

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

21781320 is a wasteful number, since it uses less digits than its factorization.

21781320 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 623 (or 619 counting only the distinct ones).

The product of its (nonzero) digits is 672, while the sum is 24.

The square root of 21781320 is about 4667.0461750448. The cubic root of 21781320 is about 279.2724308049.

The spelling of 21781320 in words is "twenty-one million, seven hundred eighty-one thousand, three hundred twenty".