51397840 has 80 divisors (see below), whose sum is σ = 130647888. Its totient is φ = 18690048.

The previous prime is 51397813. The next prime is 51397867. The reversal of 51397840 is 4879315.

It is an interprime number because it is at equal distance from previous prime (51397813) and next prime (51397867).

It can be written as a sum of positive squares in 8 ways, for example, as 760384 + 50637456 = 872^2 + 7116^2 .

It is a tau number, because it is divible by the number of its divisors (80).

It is a self number, because there is not a number n which added to its sum of digits gives 51397840.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 75582 + ... + 76258.

Almost surely, 2^51397840 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 51397840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (65323944).

51397840 is an abundant number, since it is smaller than the sum of its proper divisors (79250048).

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

51397840 is a wasteful number, since it uses less digits than its factorization.

51397840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 776 (or 770 counting only the distinct ones).

The product of its (nonzero) digits is 30240, while the sum is 37.

The square root of 51397840 is about 7169.2286893361. The cubic root of 51397840 is about 371.8047690267.

The spelling of 51397840 in words is "fifty-one million, three hundred ninety-seven thousand, eight hundred forty".