20021999981 has 2 divisors, whose sum is σ = 20021999982. Its totient is φ = 20021999980.

The previous prime is 20021999971. The next prime is 20022000017. The reversal of 20021999981 is 18999912002.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14756175625 + 5265824356 = 121475^2 + 72566^2 .

It is a cyclic number.

It is not a de Polignac number, because 20021999981 - 2¹⁰ = 20021998957 is a prime.

It is a super-2 number, since 2×20021999981² (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 (20021999941) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10010999990 + 10010999991.

It is an arithmetic number, because the mean of its divisors is an integer number (10010999991).

Almost surely, 2^20021999981 is an apocalyptic number.

It is an amenable number.

20021999981 is a deficient number, since it is larger than the sum of its proper divisors (1).

20021999981 is an equidigital number, since it uses as much as digits as its factorization.

20021999981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 209952, while the sum is 50.

The spelling of 20021999981 in words is "twenty billion, twenty-one million, nine hundred ninety-nine thousand, nine hundred eighty-one".