51891809 has 2 divisors, whose sum is σ = 51891810. Its totient is φ = 51891808.

The previous prime is 51891787. The next prime is 51891811. The reversal of 51891809 is 90819815.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 26419600 + 25472209 = 5140^2 + 5047^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-51891809 is a prime.

It is a Sophie Germain prime.

Together with 51891811, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (51891899) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 25945904 + 25945905.

It is an arithmetic number, because the mean of its divisors is an integer number (25945905).

Almost surely, 2^51891809 is an apocalyptic number.

It is an amenable number.

51891809 is a deficient number, since it is larger than the sum of its proper divisors (1).

51891809 is an equidigital number, since it uses as much as digits as its factorization.

51891809 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 25920, while the sum is 41.

The square root of 51891809 is about 7203.5969487472. The cubic root of 51891809 is about 372.9920743332.

The spelling of 51891809 in words is "fifty-one million, eight hundred ninety-one thousand, eight hundred nine".