991199966621 has 2 divisors, whose sum is σ = 991199966622. Its totient is φ = 991199966620.

The previous prime is 991199966591. The next prime is 991199966633. The reversal of 991199966621 is 126669991199.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 719561992900 + 271637973721 = 848270^2 + 521189^2 .

It is a cyclic number.

It is not a de Polignac number, because 991199966621 - 2³⁴ = 974020097437 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991199969621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495599983310 + 495599983311.

It is an arithmetic number, because the mean of its divisors is an integer number (495599983311).

Almost surely, 2^991199966621 is an apocalyptic number.

It is an amenable number.

991199966621 is a deficient number, since it is larger than the sum of its proper divisors (1).

991199966621 is an equidigital number, since it uses as much as digits as its factorization.

991199966621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 25509168, while the sum is 68.

The spelling of 991199966621 in words is "nine hundred ninety-one billion, one hundred ninety-nine million, nine hundred sixty-six thousand, six hundred twenty-one".