21989780 has 12 divisors (see below), whose sum is σ = 46178580. Its totient is φ = 8795904.

The previous prime is 21989777. The next prime is 21989797. The reversal of 21989780 is 8798912.

It can be written as a sum of positive squares in 2 ways, for example, as 14227984 + 7761796 = 3772^2 + 2786^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 549725 + ... + 549764.

It is an arithmetic number, because the mean of its divisors is an integer number (3848215).

Almost surely, 2^21989780 is an apocalyptic number.

21989780 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21989780 is an abundant number, since it is smaller than the sum of its proper divisors (24188800).

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

21989780 is a wasteful number, since it uses less digits than its factorization.

21989780 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1099498 (or 1099496 counting only the distinct ones).

The product of its (nonzero) digits is 72576, while the sum is 44.

The square root of 21989780 is about 4689.3261776080. The cubic root of 21989780 is about 280.1605371906.

The spelling of 21989780 in words is "twenty-one million, nine hundred eighty-nine thousand, seven hundred eighty".