990971981 has 2 divisors, whose sum is σ = 990971982. Its totient is φ = 990971980.

The previous prime is 990971959. The next prime is 990972011. The reversal of 990971981 is 189179099.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 496621225 + 494350756 = 22285^2 + 22234^2 .

It is an emirp because it is prime and its reverse (189179099) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 990971981 - 2¹⁰ = 990970957 is a prime.

It is a super-2 number, since 2×990971981² = 1964050934254128722, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (990971381) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495485990 + 495485991.

It is an arithmetic number, because the mean of its divisors is an integer number (495485991).

Almost surely, 2^990971981 is an apocalyptic number.

It is an amenable number.

990971981 is a deficient number, since it is larger than the sum of its proper divisors (1).

990971981 is an equidigital number, since it uses as much as digits as its factorization.

990971981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 367416, while the sum is 53.

The square root of 990971981 is about 31479.7074478147. The cubic root of 990971981 is about 996.9815585113.

The spelling of 990971981 in words is "nine hundred ninety million, nine hundred seventy-one thousand, nine hundred eighty-one".