18615936721 has 2 divisors, whose sum is σ = 18615936722. Its totient is φ = 18615936720.

The previous prime is 18615936701. The next prime is 18615936761. The reversal of 18615936721 is 12763951681.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17099223696 + 1516713025 = 130764^2 + 38945^2 .

It is a cyclic number.

It is not a de Polignac number, because 18615936721 - 2¹⁹ = 18615412433 is a prime.

It is not a weakly prime, because it can be changed into another prime (18615936701) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9307968360 + 9307968361.

It is an arithmetic number, because the mean of its divisors is an integer number (9307968361).

Almost surely, 2^18615936721 is an apocalyptic number.

It is an amenable number.

18615936721 is a deficient number, since it is larger than the sum of its proper divisors (1).

18615936721 is an equidigital number, since it uses as much as digits as its factorization.

18615936721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 544320, while the sum is 49.

The spelling of 18615936721 in words is "eighteen billion, six hundred fifteen million, nine hundred thirty-six thousand, seven hundred twenty-one".