1021396991 has 4 divisors (see below), whose sum is σ = 1021639752. Its totient is φ = 1021154232.

The previous prime is 1021396979. The next prime is 1021397051. The reversal of 1021396991 is 1996931201.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1996931201 = 1399 ⋅1427399.

It is a cyclic number.

It is not a de Polignac number, because 1021396991 - 2¹⁸ = 1021134847 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1021396291) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 114956 + ... + 123521.

It is an arithmetic number, because the mean of its divisors is an integer number (255409938).

Almost surely, 2^1021396991 is an apocalyptic number.

1021396991 is a deficient number, since it is larger than the sum of its proper divisors (242761).

1021396991 is an equidigital number, since it uses as much as digits as its factorization.

1021396991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 242760.

The product of its (nonzero) digits is 26244, while the sum is 41.

The square root of 1021396991 is about 31959.3021043952. The cubic root of 1021396991 is about 1007.0820564089.

The spelling of 1021396991 in words is "one billion, twenty-one million, three hundred ninety-six thousand, nine hundred ninety-one".