1000020991 has 2 divisors, whose sum is σ = 1000020992. Its totient is φ = 1000020990.

The previous prime is 1000020961. The next prime is 1000020997. The reversal of 1000020991 is 1990200001.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 1000020991 - 2¹³ = 1000012799 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1000020997) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 500010495 + 500010496.

It is an arithmetic number, because the mean of its divisors is an integer number (500010496).

Almost surely, 2^1000020991 is an apocalyptic number.

1000020991 is a deficient number, since it is larger than the sum of its proper divisors (1).

1000020991 is an equidigital number, since it uses as much as digits as its factorization.

1000020991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 162, while the sum is 22.

The square root of 1000020991 is about 31623.1084967939. The cubic root of 1000020991 is about 1000.0069969510.

Adding to 1000020991 its reverse (1990200001), we get a palindrome (2990220992).

The spelling of 1000020991 in words is "one billion, twenty thousand, nine hundred ninety-one".