20781865 has 16 divisors (see below), whose sum is σ = 27316800. Its totient is φ = 15083712.

The previous prime is 20781863. The next prime is 20781889. The reversal of 20781865 is 56818702.

It is a cyclic number.

It is not a de Polignac number, because 20781865 - 2¹ = 20781863 is a prime.

It is not an unprimeable number, because it can be changed into a prime (20781863) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1126 + ... + 6544.

It is an arithmetic number, because the mean of its divisors is an integer number (1707300).

Almost surely, 2^20781865 is an apocalyptic number.

It is an amenable number.

20781865 is a deficient number, since it is larger than the sum of its proper divisors (6534935).

20781865 is a wasteful number, since it uses less digits than its factorization.

20781865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5496.

The product of its (nonzero) digits is 26880, while the sum is 37.

The square root of 20781865 is about 4558.7130859487. The cubic root of 20781865 is about 274.9338242972.

The spelling of 20781865 in words is "twenty million, seven hundred eighty-one thousand, eight hundred sixty-five".