51991665 has 32 divisors (see below), whose sum is σ = 92123136. Its totient is φ = 24826560.

The previous prime is 51991663. The next prime is 51991711. The reversal of 51991665 is 56619915.

It is not a de Polignac number, because 51991665 - 2¹ = 51991663 is a prime.

It is not an unprimeable number, because it can be changed into a prime (51991663) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 8704 + ... + 13406.

It is an arithmetic number, because the mean of its divisors is an integer number (2878848).

Almost surely, 2^51991665 is an apocalyptic number.

51991665 is a gapful number since it is divisible by the number (55) formed by its first and last digit.

It is an amenable number.

51991665 is a deficient number, since it is larger than the sum of its proper divisors (40131471).

51991665 is a wasteful number, since it uses less digits than its factorization.

51991665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4789.

The product of its digits is 72900, while the sum is 42.

The square root of 51991665 is about 7210.5245995004. The cubic root of 51991665 is about 373.2311720004.

The spelling of 51991665 in words is "fifty-one million, nine hundred ninety-one thousand, six hundred sixty-five".