971511991 has 2 divisors, whose sum is σ = 971511992. Its totient is φ = 971511990.

The previous prime is 971511913. The next prime is 971512033. The reversal of 971511991 is 199115179.

It is a strong prime.

It is an emirp because it is prime and its reverse (199115179) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 971511991 - 2²¹ = 969414839 is a prime.

It is equal to p_49471891 and since 971511991 and 49471891 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (971511911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 485755995 + 485755996.

It is an arithmetic number, because the mean of its divisors is an integer number (485755996).

Almost surely, 2^971511991 is an apocalyptic number.

971511991 is a deficient number, since it is larger than the sum of its proper divisors (1).

971511991 is an equidigital number, since it uses as much as digits as its factorization.

971511991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 25515, while the sum is 43.

The square root of 971511991 is about 31169.0871056565. The cubic root of 971511991 is about 990.4123680879.

The spelling of 971511991 in words is "nine hundred seventy-one million, five hundred eleven thousand, nine hundred ninety-one".