20021221991 has 2 divisors, whose sum is σ = 20021221992. Its totient is φ = 20021221990.

The previous prime is 20021221951. The next prime is 20021222017. The reversal of 20021221991 is 19912212002.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20021221991 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20021221901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10010610995 + 10010610996.

It is an arithmetic number, because the mean of its divisors is an integer number (10010610996).

Almost surely, 2^20021221991 is an apocalyptic number.

20021221991 is a deficient number, since it is larger than the sum of its proper divisors (1).

20021221991 is an equidigital number, since it uses as much as digits as its factorization.

20021221991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1296, while the sum is 29.

Adding to 20021221991 its reverse (19912212002), we get a palindrome (39933433993).

The spelling of 20021221991 in words is "twenty billion, twenty-one million, two hundred twenty-one thousand, nine hundred ninety-one".