21381780 has 48 divisors (see below), whose sum is σ = 68423040. Its totient is φ = 4887168.

The previous prime is 21381779. The next prime is 21381791. The reversal of 21381780 is 8718312.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 25035 + ... + 25874.

It is an arithmetic number, because the mean of its divisors is an integer number (1425480).

Almost surely, 2^21381780 is an apocalyptic number.

21381780 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21381780 is an abundant number, since it is smaller than the sum of its proper divisors (47041260).

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

21381780 is a wasteful number, since it uses less digits than its factorization.

21381780 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 50928 (or 50926 counting only the distinct ones).

The product of its (nonzero) digits is 2688, while the sum is 30.

The square root of 21381780 is about 4624.0436849148. The cubic root of 21381780 is about 277.5542950331.

The spelling of 21381780 in words is "twenty-one million, three hundred eighty-one thousand, seven hundred eighty".