91821971 has 2 divisors, whose sum is σ = 91821972. Its totient is φ = 91821970.

The previous prime is 91821967. The next prime is 91821991. The reversal of 91821971 is 17912819.

It is a weak prime.

It is an emirp because it is prime and its reverse (17912819) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 91821971 - 2² = 91821967 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (91821931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 45910985 + 45910986.

It is an arithmetic number, because the mean of its divisors is an integer number (45910986).

Almost surely, 2^91821971 is an apocalyptic number.

91821971 is a deficient number, since it is larger than the sum of its proper divisors (1).

91821971 is an equidigital number, since it uses as much as digits as its factorization.

91821971 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 9072, while the sum is 38.

The square root of 91821971 is about 9582.3781494992. The cubic root of 91821971 is about 451.1443647424.

The spelling of 91821971 in words is "ninety-one million, eight hundred twenty-one thousand, nine hundred seventy-one".