20515813 has 2 divisors, whose sum is σ = 20515814. Its totient is φ = 20515812.

The previous prime is 20515811. The next prime is 20515819. The reversal of 20515813 is 31851502.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18378369 + 2137444 = 4287^2 + 1462^2 .

It is a cyclic number.

It is not a de Polignac number, because 20515813 - 2¹ = 20515811 is a prime.

Together with 20515811, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20515811) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10257906 + 10257907.

It is an arithmetic number, because the mean of its divisors is an integer number (10257907).

Almost surely, 2^20515813 is an apocalyptic number.

It is an amenable number.

20515813 is a deficient number, since it is larger than the sum of its proper divisors (1).

20515813 is an equidigital number, since it uses as much as digits as its factorization.

20515813 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1200, while the sum is 25.

The square root of 20515813 is about 4529.4384861702. The cubic root of 20515813 is about 273.7555361223.

The spelling of 20515813 in words is "twenty million, five hundred fifteen thousand, eight hundred thirteen".