81000121021991 has 2 divisors, whose sum is σ = 81000121021992. Its totient is φ = 81000121021990.

The previous prime is 81000121021969. The next prime is 81000121022053. The reversal of 81000121021991 is 19912012100018.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81000121021991 - 2¹⁰ = 81000121020967 is a prime.

It is a super-2 number, since 2×81000121021991² (a number of 29 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81000121021291) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40500060510995 + 40500060510996.

It is an arithmetic number, because the mean of its divisors is an integer number (40500060510996).

Almost surely, 2^{81000121021991} is an apocalyptic number.

81000121021991 is a deficient number, since it is larger than the sum of its proper divisors (1).

81000121021991 is an equidigital number, since it uses as much as digits as its factorization.

81000121021991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2592, while the sum is 35.

The spelling of 81000121021991 in words is "eighty-one trillion, one hundred twenty-one million, twenty-one thousand, nine hundred ninety-one".