20685780 has 90 divisors (see below), whose sum is σ = 65471406. Its totient is φ = 5467392.

The previous prime is 20685733. The next prime is 20685811. The reversal of 20685780 is 8758602.

20685780 is a `hidden beast` number, since 20 + 68 + 578 + 0 = 666.

It can be written as a sum of positive squares in 3 ways, for example, as 2178576 + 18507204 = 1476^2 + 4302^2 .

It is a tau number, because it is divible by the number of its divisors (90).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 29 ways as a sum of consecutive naturals, for example, 183004 + ... + 183116.

Almost surely, 2^20685780 is an apocalyptic number.

20685780 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 20685780, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32735703).

20685780 is an abundant number, since it is smaller than the sum of its proper divisors (44785626).

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

20685780 is a wasteful number, since it uses less digits than its factorization.

20685780 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 247 (or 123 counting only the distinct ones).

The product of its (nonzero) digits is 26880, while the sum is 36.

The square root of 20685780 is about 4548.1622662346. The cubic root of 20685780 is about 274.5094505391.

The spelling of 20685780 in words is "twenty million, six hundred eighty-five thousand, seven hundred eighty".