21780780 has 48 divisors (see below), whose sum is σ = 69699840. Its totient is φ = 4978368.

The previous prime is 21780779. The next prime is 21780809. The reversal of 21780780 is 8708712.

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 15 ways as a sum of consecutive naturals, for example, 25510 + ... + 26349.

It is an arithmetic number, because the mean of its divisors is an integer number (1452080).

Almost surely, 2^21780780 is an apocalyptic number.

21780780 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21780780 is an abundant number, since it is smaller than the sum of its proper divisors (47919060).

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

21780780 is a wasteful number, since it uses less digits than its factorization.

21780780 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 51878 (or 51876 counting only the distinct ones).

The product of its (nonzero) digits is 6272, while the sum is 33.

The square root of 21780780 is about 4666.9883222481. The cubic root of 21780780 is about 279.2701228891.

The spelling of 21780780 in words is "twenty-one million, seven hundred eighty thousand, seven hundred eighty".