20781618257 has 4 divisors (see below), whose sum is σ = 20781945780. Its totient is φ = 20781290736.

The previous prime is 20781618241. The next prime is 20781618271. The reversal of 20781618257 is 75281618702.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 12124432321 + 8657185936 = 110111^2 + 93044^2 .

It is a cyclic number.

It is not a de Polignac number, because 20781618257 - 2⁴ = 20781618241 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20781618157) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 34658 + ... + 206795.

It is an arithmetic number, because the mean of its divisors is an integer number (5195486445).

Almost surely, 2^20781618257 is an apocalyptic number.

It is an amenable number.

20781618257 is a deficient number, since it is larger than the sum of its proper divisors (327523).

20781618257 is an equidigital number, since it uses as much as digits as its factorization.

20781618257 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 327522.

The product of its (nonzero) digits is 376320, while the sum is 47.

The spelling of 20781618257 in words is "twenty billion, seven hundred eighty-one million, six hundred eighteen thousand, two hundred fifty-seven".