20908781 has 4 divisors (see below), whose sum is σ = 20918364. Its totient is φ = 20899200.

The previous prime is 20908753. The next prime is 20908807. The reversal of 20908781 is 18780902.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 7107556 + 13801225 = 2666^2 + 3715^2 .

It is a cyclic number.

It is not a de Polignac number, because 20908781 - 2¹⁴ = 20892397 is a prime.

It is a super-2 number, since 2×20908781² = 874354245811922, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20908711) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 251 + ... + 6471.

It is an arithmetic number, because the mean of its divisors is an integer number (5229591).

Almost surely, 2^20908781 is an apocalyptic number.

It is an amenable number.

20908781 is a deficient number, since it is larger than the sum of its proper divisors (9583).

20908781 is an equidigital number, since it uses as much as digits as its factorization.

20908781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9582.

The product of its (nonzero) digits is 8064, while the sum is 35.

The square root of 20908781 is about 4572.6120543952. The cubic root of 20908781 is about 275.4923675124.

The spelling of 20908781 in words is "twenty million, nine hundred eight thousand, seven hundred eighty-one".