18720255781 has 2 divisors, whose sum is σ = 18720255782. Its totient is φ = 18720255780.

The previous prime is 18720255773. The next prime is 18720255787. The reversal of 18720255781 is 18755202781.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16840252900 + 1880002881 = 129770^2 + 43359^2 .

It is a cyclic number.

It is not a de Polignac number, because 18720255781 - 2³ = 18720255773 is a prime.

It is a super-2 number, since 2×18720255781² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18720255787) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9360127890 + 9360127891.

It is an arithmetic number, because the mean of its divisors is an integer number (9360127891).

Almost surely, 2^18720255781 is an apocalyptic number.

It is an amenable number.

18720255781 is a deficient number, since it is larger than the sum of its proper divisors (1).

18720255781 is an equidigital number, since it uses as much as digits as its factorization.

18720255781 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 313600, while the sum is 46.

The spelling of 18720255781 in words is "eighteen billion, seven hundred twenty million, two hundred fifty-five thousand, seven hundred eighty-one".