51399665 has 16 divisors (see below), whose sum is σ = 63728208. Its totient is φ = 39776256.

The previous prime is 51399661. The next prime is 51399703. The reversal of 51399665 is 56699315.

It can be written as a sum of positive squares in 8 ways, for example, as 1216609 + 50183056 = 1103^2 + 7084^2 .

It is a cyclic number.

It is not a de Polignac number, because 51399665 - 2² = 51399661 is a prime.

It is a super-2 number, since 2×51399665² = 5283851124224450, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (51399661) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 18017 + ... + 20673.

It is an arithmetic number, because the mean of its divisors is an integer number (3983013).

Almost surely, 2^51399665 is an apocalyptic number.

It is an amenable number.

51399665 is a deficient number, since it is larger than the sum of its proper divisors (12328543).

51399665 is a wasteful number, since it uses less digits than its factorization.

51399665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2788.

The product of its digits is 218700, while the sum is 44.

The square root of 51399665 is about 7169.3559682861. The cubic root of 51399665 is about 371.8091695726.

The spelling of 51399665 in words is "fifty-one million, three hundred ninety-nine thousand, six hundred sixty-five".