20991023 has 2 divisors, whose sum is σ = 20991024. Its totient is φ = 20991022.

The previous prime is 20991017. The next prime is 20991043. The reversal of 20991023 is 32019902.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 20991023 - 2⁴ = 20991007 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 20990983 and 20991001.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20991043) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10495511 + 10495512.

It is an arithmetic number, because the mean of its divisors is an integer number (10495512).

Almost surely, 2^20991023 is an apocalyptic number.

20991023 is a deficient number, since it is larger than the sum of its proper divisors (1).

20991023 is an equidigital number, since it uses as much as digits as its factorization.

20991023 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 972, while the sum is 26.

The square root of 20991023 is about 4581.5961192580. The cubic root of 20991023 is about 275.8530995552.

The spelling of 20991023 in words is "twenty million, nine hundred ninety-one thousand, twenty-three".