221021001991 has 2 divisors, whose sum is σ = 221021001992. Its totient is φ = 221021001990.

The previous prime is 221021001977. The next prime is 221021002003. The reversal of 221021001991 is 199100120122.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 221021001991 - 2¹³ = 221020993799 is a prime.

It is a super-2 number, since 2×221021001991² (a number of 23 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (221021001931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 110510500995 + 110510500996.

It is an arithmetic number, because the mean of its divisors is an integer number (110510500996).

Almost surely, 2^221021001991 is an apocalyptic number.

221021001991 is a deficient number, since it is larger than the sum of its proper divisors (1).

221021001991 is an equidigital number, since it uses as much as digits as its factorization.

221021001991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 648, while the sum is 28.

The spelling of 221021001991 in words is "two hundred twenty-one billion, twenty-one million, one thousand, nine hundred ninety-one".