51221540 has 48 divisors (see below), whose sum is σ = 113702400. Its totient is φ = 19350912.

The previous prime is 51221537. The next prime is 51221543. The reversal of 51221540 is 4512215.

It is an interprime number because it is at equal distance from previous prime (51221537) and next prime (51221543).

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 (51221543) 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, 26321 + ... + 28199.

It is an arithmetic number, because the mean of its divisors is an integer number (2368800).

Almost surely, 2^51221540 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 51221540, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (56851200).

51221540 is an abundant number, since it is smaller than the sum of its proper divisors (62480860).

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

51221540 is a wasteful number, since it uses less digits than its factorization.

51221540 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1964 (or 1962 counting only the distinct ones).

The product of its (nonzero) digits is 400, while the sum is 20.

The square root of 51221540 is about 7156.9225229843. The cubic root of 51221540 is about 371.3791722131.

Adding to 51221540 its reverse (4512215), we get a palindrome (55733755).

The spelling of 51221540 in words is "fifty-one million, two hundred twenty-one thousand, five hundred forty".