31130821 has 4 divisors (see below), whose sum is σ = 31150444. Its totient is φ = 31111200.

The previous prime is 31130809. The next prime is 31130837. The reversal of 31130821 is 12803113.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 3568321 + 27562500 = 1889^2 + 5250^2 .

It is a cyclic number.

It is not a de Polignac number, because 31130821 - 2¹³ = 31122629 is a prime.

It is a super-2 number, since 2×31130821² = 1938256032268082, which contains 22 as substring.

It is the 5580-th Hogben number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (31130861) by changing a digit.

It is a nontrivial repunit in base 5579.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 7200 + ... + 10681.

It is an arithmetic number, because the mean of its divisors is an integer number (7787611).

Almost surely, 2^31130821 is an apocalyptic number.

It is an amenable number.

31130821 is a deficient number, since it is larger than the sum of its proper divisors (19623).

31130821 is a wasteful number, since it uses less digits than its factorization.

31130821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19622.

The product of its (nonzero) digits is 144, while the sum is 19.

The square root of 31130821 is about 5579.5000672103. The cubic root of 31130821 is about 314.5793360173.

Adding to 31130821 its reverse (12803113), we get a palindrome (43933934).

The spelling of 31130821 in words is "thirty-one million, one hundred thirty thousand, eight hundred twenty-one".