991378513 has 2 divisors, whose sum is σ = 991378514. Its totient is φ = 991378512.

The previous prime is 991378489. The next prime is 991378517. The reversal of 991378513 is 315873199.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 530288784 + 461089729 = 23028^2 + 21473^2 .

It is an emirp because it is prime and its reverse (315873199) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 991378513 - 2¹³ = 991370321 is a prime.

It is not a weakly prime, because it can be changed into another prime (991378517) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495689256 + 495689257.

It is an arithmetic number, because the mean of its divisors is an integer number (495689257).

Almost surely, 2^991378513 is an apocalyptic number.

It is an amenable number.

991378513 is a deficient number, since it is larger than the sum of its proper divisors (1).

991378513 is an equidigital number, since it uses as much as digits as its factorization.

991378513 is an evil number, because the sum of its binary digits is even.

The product of its digits is 204120, while the sum is 46.

The square root of 991378513 is about 31486.1638342939. The cubic root of 991378513 is about 997.1178723203.

The spelling of 991378513 in words is "nine hundred ninety-one million, three hundred seventy-eight thousand, five hundred thirteen".