21987780 has 24 divisors (see below), whose sum is σ = 61565952. Its totient is φ = 5863392.

The previous prime is 21987737. The next prime is 21987787. The reversal of 21987780 is 8778912.

It is not an unprimeable number, because it can be changed into a prime (21987787) 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 7 ways as a sum of consecutive naturals, for example, 183172 + ... + 183291.

It is an arithmetic number, because the mean of its divisors is an integer number (2565248).

Almost surely, 2^21987780 is an apocalyptic number.

21987780 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21987780 is an abundant number, since it is smaller than the sum of its proper divisors (39578172).

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

21987780 is a wasteful number, since it uses less digits than its factorization.

21987780 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 366475 (or 366473 counting only the distinct ones).

The product of its (nonzero) digits is 56448, while the sum is 42.

The square root of 21987780 is about 4689.1129225046. The cubic root of 21987780 is about 280.1520432741.

The spelling of 21987780 in words is "twenty-one million, nine hundred eighty-seven thousand, seven hundred eighty".