51405840 has 100 divisors (see below), whose sum is σ = 178562604. Its totient is φ = 13706496.

The previous prime is 51405791. The next prime is 51405857. The reversal of 51405840 is 4850415.

It can be written as a sum of positive squares in 2 ways, for example, as 16548624 + 34857216 = 4068^2 + 5904^2 .

It is a super-2 number, since 2×51405840² = 5285120772211200, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 2514 + ... + 10446.

Almost surely, 2^51405840 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 51405840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (89281302).

51405840 is an abundant number, since it is smaller than the sum of its proper divisors (127156764).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

51405840 is a wasteful number, since it uses less digits than its factorization.

51405840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7958 (or 7943 counting only the distinct ones).

The product of its (nonzero) digits is 3200, while the sum is 27.

The square root of 51405840 is about 7169.7866077032. The cubic root of 51405840 is about 371.8240583187.

The spelling of 51405840 in words is "fifty-one million, four hundred five thousand, eight hundred forty".