31881821 has 2 divisors, whose sum is σ = 31881822. Its totient is φ = 31881820.

The previous prime is 31881799. The next prime is 31881853. The reversal of 31881821 is 12818813.

It is a happy number.

It is an a-pointer prime, because the next prime (31881853) can be obtained adding 31881821 to its sum of digits (32).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 27825625 + 4056196 = 5275^2 + 2014^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-31881821 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (31881721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15940910 + 15940911.

It is an arithmetic number, because the mean of its divisors is an integer number (15940911).

Almost surely, 2^31881821 is an apocalyptic number.

It is an amenable number.

31881821 is a deficient number, since it is larger than the sum of its proper divisors (1).

31881821 is an equidigital number, since it uses as much as digits as its factorization.

31881821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3072, while the sum is 32.

The square root of 31881821 is about 5646.3989409180. The cubic root of 31881821 is about 317.0889002223.

The spelling of 31881821 in words is "thirty-one million, eight hundred eighty-one thousand, eight hundred twenty-one".