20991121 has 2 divisors, whose sum is σ = 20991122. Its totient is φ = 20991120.

The previous prime is 20991101. The next prime is 20991149. The reversal of 20991121 is 12119902.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15492096 + 5499025 = 3936^2 + 2345^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20991121 is a prime.

It is not a weakly prime, because it can be changed into another prime (20991101) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10495560 + 10495561.

It is an arithmetic number, because the mean of its divisors is an integer number (10495561).

Almost surely, 2^20991121 is an apocalyptic number.

It is an amenable number.

20991121 is a deficient number, since it is larger than the sum of its proper divisors (1).

20991121 is an equidigital number, since it uses as much as digits as its factorization.

20991121 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 324, while the sum is 25.

The square root of 20991121 is about 4581.6068142083. The cubic root of 20991121 is about 275.8535288428.

It can be divided in two parts, 20991 and 121, that added together give a palindrome (21112).

The spelling of 20991121 in words is "twenty million, nine hundred ninety-one thousand, one hundred twenty-one".