20312561 has 2 divisors, whose sum is σ = 20312562. Its totient is φ = 20312560.

The previous prime is 20312543. The next prime is 20312563. The reversal of 20312561 is 16521302.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19536400 + 776161 = 4420^2 + 881^2 .

It is a cyclic number.

It is not a de Polignac number, because 20312561 - 2⁶ = 20312497 is a prime.

Together with 20312563, 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 (20312563) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10156280 + 10156281.

It is an arithmetic number, because the mean of its divisors is an integer number (10156281).

Almost surely, 2^20312561 is an apocalyptic number.

It is an amenable number.

20312561 is a deficient number, since it is larger than the sum of its proper divisors (1).

20312561 is an equidigital number, since it uses as much as digits as its factorization.

20312561 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 360, while the sum is 20.

The square root of 20312561 is about 4506.9458616673. The cubic root of 20312561 is about 272.8484938931.

Adding to 20312561 its reverse (16521302), we get a palindrome (36833863).

The spelling of 20312561 in words is "twenty million, three hundred twelve thousand, five hundred sixty-one".