51391440 has 120 divisors (see below), whose sum is σ = 174183048. Its totient is φ = 13578240.

The previous prime is 51391427. The next prime is 51391469. The reversal of 51391440 is 4419315.

51391440 is a `hidden beast` number, since 513 + 9 + 144 + 0 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 3283344 + 48108096 = 1812^2 + 6936^2 .

It is a tau number, because it is divible by the number of its divisors (120).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 98380 + ... + 98900.

Almost surely, 2^51391440 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 51391440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (87091524).

51391440 is an abundant number, since it is smaller than the sum of its proper divisors (122791608).

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

51391440 is a wasteful number, since it uses less digits than its factorization.

51391440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 677 (or 668 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 27.

The square root of 51391440 is about 7168.7823233796. The cubic root of 51391440 is about 371.7893361518.

The spelling of 51391440 in words is "fifty-one million, three hundred ninety-one thousand, four hundred forty".