991564681 has 2 divisors, whose sum is σ = 991564682. Its totient is φ = 991564680.

The previous prime is 991564669. The next prime is 991564709. The reversal of 991564681 is 186465199.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 805651456 + 185913225 = 28384^2 + 13635^2 .

It is an emirp because it is prime and its reverse (186465199) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 991564681 - 2¹⁵ = 991531913 is a prime.

It is a super-2 number, since 2×991564681² = 1966401033213263522, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (991564601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495782340 + 495782341.

It is an arithmetic number, because the mean of its divisors is an integer number (495782341).

Almost surely, 2^991564681 is an apocalyptic number.

It is an amenable number.

991564681 is a deficient number, since it is larger than the sum of its proper divisors (1).

991564681 is an equidigital number, since it uses as much as digits as its factorization.

991564681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 466560, while the sum is 49.

The square root of 991564681 is about 31489.1200416906. The cubic root of 991564681 is about 997.1802836728.

The spelling of 991564681 in words is "nine hundred ninety-one million, five hundred sixty-four thousand, six hundred eighty-one".