20991043 has 2 divisors, whose sum is σ = 20991044. Its totient is φ = 20991042.

The previous prime is 20991023. The next prime is 20991049. The reversal of 20991043 is 34019902.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20991043 is a prime.

It is not a weakly prime, because it can be changed into another prime (20991049) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10495521 + 10495522.

It is an arithmetic number, because the mean of its divisors is an integer number (10495522).

Almost surely, 2^20991043 is an apocalyptic number.

20991043 is a deficient number, since it is larger than the sum of its proper divisors (1).

20991043 is an equidigital number, since it uses as much as digits as its factorization.

20991043 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1944, while the sum is 28.

The square root of 20991043 is about 4581.5983019030. The cubic root of 20991043 is about 275.8531871650.

The spelling of 20991043 in words is "twenty million, nine hundred ninety-one thousand, forty-three".