989991021221 has 4 divisors (see below), whose sum is σ = 990078110700. Its totient is φ = 989903931744.

The previous prime is 989991021143. The next prime is 989991021233. The reversal of 989991021221 is 122120199989.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 602408822500 + 387582198721 = 776150^2 + 622561^2 .

It is a cyclic number.

It is not a de Polignac number, because 989991021221 - 2³⁸ = 715113114277 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (989991021421) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 43527686 + ... + 43550423.

It is an arithmetic number, because the mean of its divisors is an integer number (247519527675).

Almost surely, 2^989991021221 is an apocalyptic number.

It is an amenable number.

989991021221 is a deficient number, since it is larger than the sum of its proper divisors (87089479).

989991021221 is a wasteful number, since it uses less digits than its factorization.

989991021221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 87089478.

The product of its (nonzero) digits is 419904, while the sum is 53.

The spelling of 989991021221 in words is "nine hundred eighty-nine billion, nine hundred ninety-one million, twenty-one thousand, two hundred twenty-one".