991000010101021 has 2 divisors, whose sum is σ = 991000010101022. Its totient is φ = 991000010101020.

The previous prime is 991000010100983. The next prime is 991000010101039. The reversal of 991000010101021 is 120101010000199.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 899007933538521 + 91992076562500 = 29983461^2 + 9591250^2 .

It is an emirp because it is prime and its reverse (120101010000199) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-991000010101021 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991000010101421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495500005050510 + 495500005050511.

It is an arithmetic number, because the mean of its divisors is an integer number (495500005050511).

Almost surely, 2^{991000010101021} is an apocalyptic number.

It is an amenable number.

991000010101021 is a deficient number, since it is larger than the sum of its proper divisors (1).

991000010101021 is an equidigital number, since it uses as much as digits as its factorization.

991000010101021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 162, while the sum is 25.

The spelling of 991000010101021 in words is "nine hundred ninety-one trillion, ten million, one hundred one thousand, twenty-one".