991947961 has 2 divisors, whose sum is σ = 991947962. Its totient is φ = 991947960.

The previous prime is 991947959. The next prime is 991947997. The reversal of 991947961 is 169749199.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 911738025 + 80209936 = 30195^2 + 8956^2 .

It is a cyclic number.

It is not a de Polignac number, because 991947961 - 2¹ = 991947959 is a prime.

Together with 991947959, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (991947941) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495973980 + 495973981.

It is an arithmetic number, because the mean of its divisors is an integer number (495973981).

Almost surely, 2^991947961 is an apocalyptic number.

It is an amenable number.

991947961 is a deficient number, since it is larger than the sum of its proper divisors (1).

991947961 is an equidigital number, since it uses as much as digits as its factorization.

991947961 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1102248, while the sum is 55.

The square root of 991947961 is about 31495.2053652616. The cubic root of 991947961 is about 997.3087506745.

The spelling of 991947961 in words is "nine hundred ninety-one million, nine hundred forty-seven thousand, nine hundred sixty-one".