31878027721 has 2 divisors, whose sum is σ = 31878027722. Its totient is φ = 31878027720.

The previous prime is 31878027719. The next prime is 31878027763. The reversal of 31878027721 is 12772087813.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 29797664400 + 2080363321 = 172620^2 + 45611^2 .

It is a cyclic number.

It is not a de Polignac number, because 31878027721 - 2¹ = 31878027719 is a prime.

Together with 31878027719, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (31878027121) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 15939013860 + 15939013861.

It is an arithmetic number, because the mean of its divisors is an integer number (15939013861).

Almost surely, 2^31878027721 is an apocalyptic number.

It is an amenable number.

31878027721 is a deficient number, since it is larger than the sum of its proper divisors (1).

31878027721 is an equidigital number, since it uses as much as digits as its factorization.

31878027721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 263424, while the sum is 46.

The spelling of 31878027721 in words is "thirty-one billion, eight hundred seventy-eight million, twenty-seven thousand, seven hundred twenty-one".