51131221 has 4 divisors (see below), whose sum is σ = 51145612. Its totient is φ = 51116832.

The previous prime is 51131219. The next prime is 51131243. The reversal of 51131221 is 12213115.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 1920996 + 49210225 = 1386^2 + 7015^2 .

It is a cyclic number.

It is not a de Polignac number, because 51131221 - 2¹ = 51131219 is a prime.

It is a super-2 number, since 2×51131221² = 5228803521901682, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 51131195 and 51131204.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (51131021) 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, 2401 + ... + 10393.

It is an arithmetic number, because the mean of its divisors is an integer number (12786403).

Almost surely, 2^51131221 is an apocalyptic number.

It is an amenable number.

51131221 is a deficient number, since it is larger than the sum of its proper divisors (14391).

51131221 is an equidigital number, since it uses as much as digits as its factorization.

51131221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14390.

The product of its digits is 60, while the sum is 16.

The square root of 51131221 is about 7150.6098341330. The cubic root of 51131221 is about 371.1607593473.

Adding to 51131221 its reverse (12213115), we get a palindrome (63344336).

The spelling of 51131221 in words is "fifty-one million, one hundred thirty-one thousand, two hundred twenty-one".