20661840 has 60 divisors (see below), whose sum is σ = 69391764. Its totient is φ = 5509632.

The previous prime is 20661821. The next prime is 20661857. The reversal of 20661840 is 4816602.

20661840 is a `hidden beast` number, since 2 + 0 + 6 + 618 + 40 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 4210704 + 16451136 = 2052^2 + 4056^2 .

It is a tau number, because it is divible by the number of its divisors (60).

It is a congruent number.

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 11 ways as a sum of consecutive naturals, for example, 13629 + ... + 15068.

Almost surely, 2^20661840 is an apocalyptic number.

20661840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20661840 is an abundant number, since it is smaller than the sum of its proper divisors (48729924).

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

20661840 is a wasteful number, since it uses less digits than its factorization.

20661840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 28716 (or 28707 counting only the distinct ones).

The product of its (nonzero) digits is 2304, while the sum is 27.

The square root of 20661840 is about 4545.5296721064. The cubic root of 20661840 is about 274.4035115305.

The spelling of 20661840 in words is "twenty million, six hundred sixty-one thousand, eight hundred forty".