20209691 has 2 divisors, whose sum is σ = 20209692. Its totient is φ = 20209690.

The previous prime is 20209681. The next prime is 20209741. The reversal of 20209691 is 19690202.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 20209691 - 2¹⁸ = 19947547 is a prime.

It is a super-2 number, since 2×20209691² = 816863220630962, which contains 22 as substring.

It is a Sophie Germain prime.

It is not a weakly prime, because it can be changed into another prime (20209681) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10104845 + 10104846.

It is an arithmetic number, because the mean of its divisors is an integer number (10104846).

Almost surely, 2^20209691 is an apocalyptic number.

20209691 is a deficient number, since it is larger than the sum of its proper divisors (1).

20209691 is an equidigital number, since it uses as much as digits as its factorization.

20209691 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 29.

The square root of 20209691 is about 4495.5189911733. The cubic root of 20209691 is about 272.3871136943.

Adding to 20209691 its reverse (19690202), we get a palindrome (39899893).

It can be divided in two parts, 2020 and 9691, that added together give a palindrome (11711).

The spelling of 20209691 in words is "twenty million, two hundred nine thousand, six hundred ninety-one".