991199969621 has 2 divisors, whose sum is σ = 991199969622. Its totient is φ = 991199969620.

The previous prime is 991199969609. The next prime is 991199969623. The reversal of 991199969621 is 126969991199.

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., 717790200625 + 273409768996 = 847225^2 + 522886^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-991199969621 is a prime.

Together with 991199969623, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991199969623) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495599984810 + 495599984811.

It is an arithmetic number, because the mean of its divisors is an integer number (495599984811).

Almost surely, 2^991199969621 is an apocalyptic number.

It is an amenable number.

991199969621 is a deficient number, since it is larger than the sum of its proper divisors (1).

991199969621 is an equidigital number, since it uses as much as digits as its factorization.

991199969621 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 38263752, while the sum is 71.

The spelling of 991199969621 in words is "nine hundred ninety-one billion, one hundred ninety-nine million, nine hundred sixty-nine thousand, six hundred twenty-one".