990881921 has 2 divisors, whose sum is σ = 990881922. Its totient is φ = 990881920.

The previous prime is 990881917. The next prime is 990881959. The reversal of 990881921 is 129188099.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 623201296 + 367680625 = 24964^2 + 19175^2 .

It is an emirp because it is prime and its reverse (129188099) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 990881921 - 2² = 990881917 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (990883921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495440960 + 495440961.

It is an arithmetic number, because the mean of its divisors is an integer number (495440961).

Almost surely, 2^990881921 is an apocalyptic number.

It is an amenable number.

990881921 is a deficient number, since it is larger than the sum of its proper divisors (1).

990881921 is an equidigital number, since it uses as much as digits as its factorization.

990881921 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 93312, while the sum is 47.

The square root of 990881921 is about 31478.2769699995. The cubic root of 990881921 is about 996.9513555453.

The spelling of 990881921 in words is "nine hundred ninety million, eight hundred eighty-one thousand, nine hundred twenty-one".