20201221981 has 2 divisors, whose sum is σ = 20201221982. Its totient is φ = 20201221980.

The previous prime is 20201221973. The next prime is 20201221993. The reversal of 20201221981 is 18912210202.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11499130756 + 8702091225 = 107234^2 + 93285^2 .

It is a cyclic number.

It is not a de Polignac number, because 20201221981 - 2³ = 20201221973 is a prime.

It is a super-2 number, since 2×20201221981² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20201221921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10100610990 + 10100610991.

It is an arithmetic number, because the mean of its divisors is an integer number (10100610991).

Almost surely, 2^20201221981 is an apocalyptic number.

It is an amenable number.

20201221981 is a deficient number, since it is larger than the sum of its proper divisors (1).

20201221981 is an equidigital number, since it uses as much as digits as its factorization.

20201221981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1152, while the sum is 28.

The spelling of 20201221981 in words is "twenty billion, two hundred one million, two hundred twenty-one thousand, nine hundred eighty-one".