990891221 has 4 divisors (see below), whose sum is σ = 1033973472. Its totient is φ = 947808972.

The previous prime is 990891203. The next prime is 990891229. The reversal of 990891221 is 122198099.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-990891221 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 (990891229) 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, 21541091 + ... + 21541136.

It is an arithmetic number, because the mean of its divisors is an integer number (258493368).

Almost surely, 2^990891221 is an apocalyptic number.

It is an amenable number.

990891221 is a deficient number, since it is larger than the sum of its proper divisors (43082251).

990891221 is a wasteful number, since it uses less digits than its factorization.

990891221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 43082250.

The product of its (nonzero) digits is 23328, while the sum is 41.

The square root of 990891221 is about 31478.4246905718. The cubic root of 990891221 is about 996.9544745239.

The spelling of 990891221 in words is "nine hundred ninety million, eight hundred ninety-one thousand, two hundred twenty-one".