51139987 has 4 divisors (see below), whose sum is σ = 52789696. Its totient is φ = 49490280.

The previous prime is 51139981. The next prime is 51139999. The reversal of 51139987 is 78993115.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 51139987 - 2¹¹ = 51137939 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (51139981) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 824808 + ... + 824869.

It is an arithmetic number, because the mean of its divisors is an integer number (13197424).

Almost surely, 2^51139987 is an apocalyptic number.

51139987 is a deficient number, since it is larger than the sum of its proper divisors (1649709).

51139987 is a wasteful number, since it uses less digits than its factorization.

51139987 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1649708.

The product of its digits is 68040, while the sum is 43.

The square root of 51139987 is about 7151.2227625770. Note that the first 3 decimals coincide. The cubic root of 51139987 is about 371.1819688890.

The spelling of 51139987 in words is "fifty-one million, one hundred thirty-nine thousand, nine hundred eighty-seven".