991978139 has 2 divisors, whose sum is σ = 991978140. Its totient is φ = 991978138.

The previous prime is 991978073. The next prime is 991978171. The reversal of 991978139 is 931879199.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 991978139 - 2²⁸ = 723542683 is a prime.

It is not a weakly prime, because it can be changed into another prime (991978199) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495989069 + 495989070.

It is an arithmetic number, because the mean of its divisors is an integer number (495989070).

Almost surely, 2^991978139 is an apocalyptic number.

991978139 is a deficient number, since it is larger than the sum of its proper divisors (1).

991978139 is an equidigital number, since it uses as much as digits as its factorization.

991978139 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1102248, while the sum is 56.

The square root of 991978139 is about 31495.6844504132. The cubic root of 991978139 is about 997.3188642690.

The spelling of 991978139 in words is "nine hundred ninety-one million, nine hundred seventy-eight thousand, one hundred thirty-nine".