20309561 has 2 divisors, whose sum is σ = 20309562. Its totient is φ = 20309560.

The previous prime is 20309551. The next prime is 20309567. The reversal of 20309561 is 16590302.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13366336 + 6943225 = 3656^2 + 2635^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20309561 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 20309561.

It is not a weakly prime, because it can be changed into another prime (20309567) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10154780 + 10154781.

It is an arithmetic number, because the mean of its divisors is an integer number (10154781).

Almost surely, 2^20309561 is an apocalyptic number.

It is an amenable number.

20309561 is a deficient number, since it is larger than the sum of its proper divisors (1).

20309561 is an equidigital number, since it uses as much as digits as its factorization.

20309561 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1620, while the sum is 26.

The square root of 20309561 is about 4506.6130297597. The cubic root of 20309561 is about 272.8350607308.

Adding to 20309561 its reverse (16590302), we get a palindrome (36899863).

The spelling of 20309561 in words is "twenty million, three hundred nine thousand, five hundred sixty-one".