20721131 has 2 divisors, whose sum is σ = 20721132. Its totient is φ = 20721130.

The previous prime is 20721101. The next prime is 20721133. The reversal of 20721131 is 13112702.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 20721131 - 2¹⁰ = 20720107 is a prime.

It is a super-2 number, since 2×20721131² = 858730539838322, which contains 22 as substring.

It is a Sophie Germain prime.

Together with 20721133, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (20721133) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10360565 + 10360566.

It is an arithmetic number, because the mean of its divisors is an integer number (10360566).

Almost surely, 2^20721131 is an apocalyptic number.

20721131 is a deficient number, since it is larger than the sum of its proper divisors (1).

20721131 is an equidigital number, since it uses as much as digits as its factorization.

20721131 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 84, while the sum is 17.

The square root of 20721131 is about 4552.0469022188. The cubic root of 20721131 is about 274.6657360137.

Adding to 20721131 its reverse (13112702), we get a palindrome (33833833).

It can be divided in two parts, 2072 and 1131, that multiplied together give a palindrome (2343432).

The spelling of 20721131 in words is "twenty million, seven hundred twenty-one thousand, one hundred thirty-one".