18511720991 has 2 divisors, whose sum is σ = 18511720992. Its totient is φ = 18511720990.

The previous prime is 18511720961. The next prime is 18511721009. The reversal of 18511720991 is 19902711581.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18511720991 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18511720901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9255860495 + 9255860496.

It is an arithmetic number, because the mean of its divisors is an integer number (9255860496).

Almost surely, 2^18511720991 is an apocalyptic number.

18511720991 is a deficient number, since it is larger than the sum of its proper divisors (1).

18511720991 is an equidigital number, since it uses as much as digits as its factorization.

18511720991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 45360, while the sum is 44.

The spelling of 18511720991 in words is "eighteen billion, five hundred eleven million, seven hundred twenty thousand, nine hundred ninety-one".