18661528721 has 16 divisors (see below), whose sum is σ = 20464315200. Its totient is φ = 16876691520.

The previous prime is 18661528709. The next prime is 18661528747. The reversal of 18661528721 is 12782516681.

It is a cyclic number.

It is not a de Polignac number, because 18661528721 - 2¹⁰ = 18661527697 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18661528751) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1695191 + ... + 1706163.

It is an arithmetic number, because the mean of its divisors is an integer number (1279019700).

Almost surely, 2^18661528721 is an apocalyptic number.

18661528721 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

18661528721 is a deficient number, since it is larger than the sum of its proper divisors (1802786479).

18661528721 is a wasteful number, since it uses less digits than its factorization.

18661528721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11776.

The product of its digits is 322560, while the sum is 47.

The spelling of 18661528721 in words is "eighteen billion, six hundred sixty-one million, five hundred twenty-eight thousand, seven hundred twenty-one".