51721640 has 64 divisors (see below), whose sum is σ = 122549760. Its totient is φ = 19618560.

The previous prime is 51721627. The next prime is 51721643. The reversal of 51721640 is 4612715.

It is not an unprimeable number, because it can be changed into a prime (51721643) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 65327 + ... + 66113.

It is an arithmetic number, because the mean of its divisors is an integer number (1914840).

Almost surely, 2^51721640 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 51721640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (61274880).

51721640 is an abundant number, since it is smaller than the sum of its proper divisors (70828120).

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

51721640 is a wasteful number, since it uses less digits than its factorization.

51721640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 882 (or 878 counting only the distinct ones).

The product of its (nonzero) digits is 1680, while the sum is 26.

The square root of 51721640 is about 7191.7758585762. The cubic root of 51721640 is about 372.5839097488.

The spelling of 51721640 in words is "fifty-one million, seven hundred twenty-one thousand, six hundred forty".