18994187521 has 2 divisors, whose sum is σ = 18994187522. Its totient is φ = 18994187520.

The previous prime is 18994187489. The next prime is 18994187551. The reversal of 18994187521 is 12578149981.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17387059600 + 1607127921 = 131860^2 + 40089^2 .

It is an emirp because it is prime and its reverse (12578149981) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18994187521 - 2⁵ = 18994187489 is a prime.

It is not a weakly prime, because it can be changed into another prime (18994187551) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9497093760 + 9497093761.

It is an arithmetic number, because the mean of its divisors is an integer number (9497093761).

Almost surely, 2^18994187521 is an apocalyptic number.

It is an amenable number.

18994187521 is a deficient number, since it is larger than the sum of its proper divisors (1).

18994187521 is an equidigital number, since it uses as much as digits as its factorization.

18994187521 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1451520, while the sum is 55.

The spelling of 18994187521 in words is "eighteen billion, nine hundred ninety-four million, one hundred eighty-seven thousand, five hundred twenty-one".