20781746 has 4 divisors (see below), whose sum is σ = 31172622. Its totient is φ = 10390872.

The previous prime is 20781743. The next prime is 20781773. The reversal of 20781746 is 64718702.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 64718702 = 2 ⋅32359351.

It can be written as a sum of positive squares in only one way, i.e., 13432225 + 7349521 = 3665^2 + 2711^2 .

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (20781743) 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 as a sum of consecutive naturals, namely, 5195435 + ... + 5195438.

Almost surely, 2^20781746 is an apocalyptic number.

20781746 is a deficient number, since it is larger than the sum of its proper divisors (10390876).

20781746 is a wasteful number, since it uses less digits than its factorization.

20781746 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10390875.

The product of its (nonzero) digits is 18816, while the sum is 35.

The square root of 20781746 is about 4558.7000340009. The cubic root of 20781746 is about 274.9332995258.

The spelling of 20781746 in words is "twenty million, seven hundred eighty-one thousand, seven hundred forty-six".