9918021205521 has 135 divisors (see below), whose sum is σ = 17641420679883. Its totient is φ = 5546275843680.

The previous prime is 9918021205481. The next prime is 9918021205537. The reversal of 9918021205521 is 1255021208199.

It is a happy number.

The square root of 9918021205521 is 3149289.

It is a perfect power (a square), and thus also a powerful number.

9918021205521 is a `hidden beast` number, since 9 + 9 + 1 + 80 + 2 + 12 + 0 + 552 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 1467162900225 + 8450858305296 = 1211265^2 + 2907036^2 .

It is not a de Polignac number, because 9918021205521 - 2⁹ = 9918021205009 is a prime.

It is not an unprimeable number, because it can be changed into a prime (9918021205321) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 134 ways as a sum of consecutive naturals, for example, 4053133720 + ... + 4053136166.

Almost surely, 2^{9918021205521} is an apocalyptic number.

9918021205521 is the 3149289-th square number.

9918021205521 is the 1574645-th centered octagonal number.

It is an amenable number.

9918021205521 is a deficient number, since it is larger than the sum of its proper divisors (7723399474362).

9918021205521 is an equidigital number, since it uses as much as digits as its factorization.

9918021205521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4954 (or 2474 counting only the distinct ones).

The product of its (nonzero) digits is 129600, while the sum is 45.

The spelling of 9918021205521 in words is "nine trillion, nine hundred eighteen billion, twenty-one million, two hundred five thousand, five hundred twenty-one".