72021991 has 2 divisors, whose sum is σ = 72021992. Its totient is φ = 72021990.

The previous prime is 72021977. The next prime is 72021997. The reversal of 72021991 is 19912027.

It is a strong prime.

It is an emirp because it is prime and its reverse (19912027) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 72021991 - 2⁹ = 72021479 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (72021997) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 36010995 + 36010996.

It is an arithmetic number, because the mean of its divisors is an integer number (36010996).

Almost surely, 2^72021991 is an apocalyptic number.

72021991 is a deficient number, since it is larger than the sum of its proper divisors (1).

72021991 is an equidigital number, since it uses as much as digits as its factorization.

72021991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2268, while the sum is 31.

The square root of 72021991 is about 8486.5771074091. The cubic root of 72021991 is about 416.0591150428.

The spelling of 72021991 in words is "seventy-two million, twenty-one thousand, nine hundred ninety-one".