51213440 has 32 divisors (see below), whose sum is σ = 122433660. Its totient is φ = 20485120.

The previous prime is 51213427. The next prime is 51213443. The reversal of 51213440 is 4431215.

It can be written as a sum of positive squares in 2 ways, for example, as 43771456 + 7441984 = 6616^2 + 2728^2 .

It is a tau number, because it is divible by the number of its divisors (32).

It is a Harshad number since it is a multiple of its sum of digits (20).

It is not an unprimeable number, because it can be changed into a prime (51213443) 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, 39371 + ... + 40650.

Almost surely, 2^51213440 is an apocalyptic number.

It is an amenable number.

51213440 is an abundant number, since it is smaller than the sum of its proper divisors (71220220).

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

51213440 is an equidigital number, since it uses as much as digits as its factorization.

51213440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 80040 (or 80028 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 20.

The square root of 51213440 is about 7156.3566149263. The cubic root of 51213440 is about 371.3595949683.

Adding to 51213440 its reverse (4431215), we get a palindrome (55644655).

The spelling of 51213440 in words is "fifty-one million, two hundred thirteen thousand, four hundred forty".