21786780 has 48 divisors (see below), whose sum is σ = 61437600. Its totient is φ = 5768448.

The previous prime is 21786757. The next prime is 21786781. The reversal of 21786780 is 8768712.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21786781) by changing a digit.

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 15 ways as a sum of consecutive naturals, for example, 7722 + ... + 10158.

It is an arithmetic number, because the mean of its divisors is an integer number (1279950).

Almost surely, 2^21786780 is an apocalyptic number.

21786780 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 21786780, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30718800).

21786780 is an abundant number, since it is smaller than the sum of its proper divisors (39650820).

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

21786780 is a wasteful number, since it uses less digits than its factorization.

21786780 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2598 (or 2596 counting only the distinct ones).

The product of its (nonzero) digits is 37632, while the sum is 39.

The square root of 21786780 is about 4667.6310908211. The cubic root of 21786780 is about 279.2957642558.

The spelling of 21786780 in words is "twenty-one million, seven hundred eighty-six thousand, seven hundred eighty".