51990209 has 2 divisors, whose sum is σ = 51990210. Its totient is φ = 51990208.

The previous prime is 51990203. The next prime is 51990221. The reversal of 51990209 is 90209915.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 50452609 + 1537600 = 7103^2 + 1240^2 .

It is a cyclic number.

It is not a de Polignac number, because 51990209 - 2¹⁶ = 51924673 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (51990203) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 25995104 + 25995105.

It is an arithmetic number, because the mean of its divisors is an integer number (25995105).

Almost surely, 2^51990209 is an apocalyptic number.

It is an amenable number.

51990209 is a deficient number, since it is larger than the sum of its proper divisors (1).

51990209 is an equidigital number, since it uses as much as digits as its factorization.

51990209 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 7290, while the sum is 35.

The square root of 51990209 is about 7210.4236352658. The cubic root of 51990209 is about 373.2276879185.

The spelling of 51990209 in words is "fifty-one million, nine hundred ninety thousand, two hundred nine".